Multicomponent Structures Having Improved Adhesion Between Components

ABSTRACT

The present invention includes a multicomponent structure comprising at least two components having a tie layer or adhesive layer directly between them, the tie layer comprising at least one olefin unsaturated ester copolymer and at least one photoinitiator and optionally a crosslinking enhancer. The tie layer is preferably irradiated with sufficient actinic radiation to result in increased interlayer adhesion strength between the two components as compared with the interlayer adhesion strength before treatment with the actinic radiation or between the components having a tie layer of the same composition except without the added photoinitiator or crosslinking enhancer. Without the photoinitiator, optionally crosslinking enhancer, and radiation the interlayer adhesion of the components is preferably less than 55 N/m. At least one of the components (first component or layer) preferably comprises a halopolymer, more preferably vinylidene chloride polymer, most preferably at least a majority of a vinyl idene chloride polymer. In another embodiment, at least one component exhibits interlayer adhesion strength similar to vinylidene chloride polymers. The structure optionally is or comprises such structures as a multilayer film, bag, or package, a lined or composite pipe, or other structure having more than one component. The tie layer is advantageously irradiated with an amount of UV light effective to increase the adhesion strength between the first and second components.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/560,531, filed Apr. 8, 2004.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

This invention relates to multicomponent structures; and moreparticularly to multicomponent structures having improved adhesion.

DESCRIPTION OF THE PRIOR ART

Multicomponent structures often offer advantages of different propertiesexhibited by the various components in the structure. Multicomponentstructures include multilayer films in which different layers havespecific characteristics as well as sheets, lidstock, and containers,for example, pouches, tubes and bags. In particular, there is a need formulticomponent structures, particularly multilayer films and structuresincluding packaging useful in high temperature applications such as bagssuitable for hot-fill or in which foodstuffs can be cooked either at thetime of packaging or by the consumer, for example, immersion in hotwater or exposure to steam. Such thermal processing often is referred toas cook-in, and films used in such processes are known as cook-in films.

A cook-in or hot-fill film is preferably capable of withstandingexposure to elevated temperature conditions suitable for cooking orfilling for periods of time appropriated to cooking or filling withoutcompromising its ability to contain the food product. This could rangefrom brief contact with hot foods for filling to up to 12 hours in slowcooking conditions of 125° C. and greater, depending on the specificapplication. During such extended periods of time at elevatedtemperatures, a package formed from a cook-in film would preferablyresist failure (that is, delamination or pulling apart either at seamsor, especially, interfaces between layers).

Products such as foods are often oxygen, moisture or aroma sensitive. Insuch applications the multicomponent structures, preferably multilayerfilm structures containing the products need to include one or moreoxygen, moisture or gas barrier layers. Preferably, these barrier layersinclude vinylidene chloride polymers which are known to provideexcellent barrier properties.

Other properties of vinylidene chloride polymers, and often of otherpolymers involved in multicomponent structures, render interlayeradhesion between such polymers and polymers of many differingcompositions difficult. For instance, those skilled in the art recognizethat even in coextruded multi layer films having at least one vinylidenechloride polymer layer, that layer may not adhere sufficiently topolymers such as polyethylene especially when the multilayer films areexposed to elevated temperatures, or handling such as hot-fill orretort.

Intermediate layers between adjacent polymer layers are often used toimprove adhesion, decrease delamination or both. These layers arereferred to as tie layers or bonding layers. Sometimes tie layerscontain blends of polymers, each compatible with an adjacent layer.Alternatively, a polymer which adheres to both adjacent layers is used.For instance, copolymers of ethylene with an ester monomer such asethylene vinyl acetate (EVA) and ethylene methyl acrylate (EMA) havebeen used as tie layers between vinylidene chloride polymer layers andlayers of other compositions such as ethylene polymers or propylenepolymers. However, these tie layers may not provide sufficient adhesionat elevated temperatures. Failure can occur during the hot-filloperations, especially during the packaging operations when hot contentsare in contact with the package. In retort applications, failure is morecommon while the package is heated near retort temperatures or duringpost-retort handling or processing steps. It would be desirable toincrease the interlayer adhesion over that exhibited by these tielayers, preferably such that less delamination would occur afterhot-fill, cook-in bag, or retort use.

SUMMARY OF THE INVENTION

In one aspect, the present invention includes a multicomponent structurecomprising at least two components having a tie layer or adhesive layerdirectly between them, the tie layer comprising at least one olefinunsaturated ester copolymer and at least one photoinitiator andoptionally a crosslinking enhancer. The tie layer is preferablyirradiated with sufficient actinic radiation to result in increasedinterlayer adhesion strength between the two components as compared withthe interlayer adhesion strength before treatment with the actinicradiation or between the components having a tie layer of the samecomposition except without the added photoinitiator or crosslinkingenhancer. Without the photoinitiator, optionally crosslinking enhancer,and radiation the interlayer adhesion strength of the components ispreferably less than 55 N/m measured at 93° C. according to theprocedures of ASTM F904-98. At least one of the components (firstcomponent or layer) preferably comprises a halopolymer, more preferablyvinylidene chloride polymer, most preferably at least a majority of avinylidene chloride polymer. In another embodiment, at least onecomponent exhibits interlayer adhesion strength similar to that of avinylidene chloride polymer. The structure optionally is or comprisessuch structures as a multilayer film, bag, or package, a lined orcomposite pipe, or other structure having more than one component. Thetie layer is irradiated with an amount of UV light effective to increasethe adhesion strength between the first and second components.

In another aspect, the invention includes a tie layer compositioncomprising at least one olefin unsaturated ester copolymer and aneffective amount of at least one photoinitiator directly between a firstand a second component wherein the first component comprises avinylidene chloride polymer (hereinafter PVDC component), which tielayer, after UV irradiation, increases the adhesion strength between thecomponents measured at 93° C. at least 20 percent as compared with thesame components having a tie layer of the same configuration andcomposition except without photoinitiator and irradiation.

In yet another aspect, the invention includes a multicomponent structurecomprising at least two components, a first and a second component,having a tie layer directly between them, the tie layer comprising atleast one olefin unsaturated ester copolymer and at least onephotoinitiator, wherein at least the first component includes a majorityof a vinylidene chloride polymer or combination of vinylidene chloridepolymers (hereinafter PVDC component) wherein the structure hasincreased interlayer adhesion after irradiation with UV radiation ascompared with the interlayer adhesion strength before treatment with theUV radiation.

In another aspect, the invention includes a multicomponent structurecomprising at least two components, a first and a second component,having a tie layer directly between them, the tie layer comprising atleast one olefin unsaturated ester copolymer and at least onephotoinitiator wherein the components in the presence of the tie layerhave an adhesion strength measured according to ASTM F904-98 at 93° C.of at least 50 N/m after the structure has been irradiated with UVradiation, as compared with an adhesion strength of less than 40 N/m forcomponents and tie layer of the same composition except without thephotoinitiator and irradiation.

In another aspect, the invention includes a multicomponent structurehaving: (a) at least one first polymer component comprising at least amajority of a halopolymer having an adhesion strength with the secondcomponent and tie layer in the substantial absence of photoinitiator andUV radiation measured according to ASTM F904-98 at 93° C. of less than55 N/m; and directly adjacent to the first polymer component (b) atleast one tie layer comprising at least one olefin unsaturated estercopolymer and at least one photoinitiator; and directly adjacent to thetie layer on the side opposite the first polymer component (c) at leastone second component comprising at least one polymer, glass, silica,paper, metal, fabric or combination thereof.

In another aspect, the invention includes a film comprising a pluralityof superimposed coextruded layers; the layers comprising a first layerand a second layer and directly between the first and second layers athird layer comprising a base polymer having at least one olefinunsaturated ester copolymer and at least one photoinitiator; wherein thefirst layer comprises at least a majority by weight of at least onevinylidene chloride copolymer and wherein the film is irradiated withsufficient UV actinic radiation to increase adhesion strength betweenthe first and second layer as compared with the adhesion strength beforeirradiation.

In another aspect, the invention includes a method of cooking a foodproduct comprising:

a) substantially completely surrounding the food product in thecomposition, structure, or film of any aspect of this invention to forma packaged food product; andb) subjecting the packaged food product to an elevated temperaturesufficient to cook the food product, wherein the film does notspontaneously delaminate after the step of subjecting the packaged foodproduct to an elevated temperature.

In another aspect, the invention includes a method for adhering a firstlayer to a second layer in a film comprising a plurality of superimposedlayers, the method comprising 1) coextruding a first layer, a secondlayer comprising at least 80 percent of a vinylidene chloride polymer,and directly between them a third layer comprising a base polymer havingat least one olefin unsaturated ester copolymer and at least onephotoinitiator 2) forming a film and 3) irradiating the film with UVlight sufficiently to increase the adhesion strength between the firstand second layers.

In another aspect, the invention includes an improvement in making amultilayer, heat shrinkable film having a first layer comprising avinylidene chloride copolymer and a second layer comprising a polymer,the improvement comprising providing a tie layer directly between thefirst and second comprising at least one olefin unsaturated estercopolymer and at least one photoinitiator and irradiating the tie layerto improve the adhesion between the first and second layers.

In another aspect, the invention includes a method for improving theadhesion between a first layer or structure comprising a vinylidenechloride polymer and a contiguous second layer or structure of the sameor different composition, wherein the method includes interposingdirectly between the first and second layer a composition comprising atleast one olefin unsaturated ester copolymer and at least onephotoinitiator and irradiating the composition with sufficient UVradiation to increase the adhesion.

In another aspect, the invention includes the use of a compositioncomprising at least one olefin unsaturated ester copolymer and at leastone photoinitiator as a tie layer directly between a first component anda second component which tie layer, after irradiation, increases theadhesion strength between the components from less than 40 N/m togreater than 55 N/m.

The invention also includes the use in place of the first component orlayer comprising at least one vinylidene chloride polymer, a componentor layer of a composition having interfacial adhesion strength such thatthe interlayer adhesion strength between it and the second layer orcomponent on the other side of the tie layer composition comprising atleast one olefin unsaturated ester copolymer and at least onephotoinitiator is less than 40 N/m before irradiation and at least 50N/m after UV irradiation particularly where the difference betweenadhesion strengths is at least 20 N/m.

In an alternative aspect, the invention is a multilayer film comprising:a) a first outer layer comprising a polymer comprising mer units derivedfrom propylene; b) a second outer layer; and disposed between the firstand second outer layers, c) a barrier inner layer comprising a polymerwith a low permeance to oxygen and at least one tie layer between thebarrier layer and at least one layer adjacent thereto; wherein the tielayer or layers comprise a base polymer having at least one olefinunsaturated ester copolymer and at least one photoinitiator; wherein thetie layer or layers are irradiated to the extent that the layersdirectly adjacent the tie layer or layers exhibit at least 50 percentfewer failures due to spontaneous delamination after commercialprocessing which involves exposure to temperatures of at least 65° C.for a period of at least 1 minute as compared with a multilayer film ofthe same components and structure but without the photoinitiator or theirradiation. Hot fill and retort processes are examples of commercialprocessing. Preferably the temperature exposure is to at least 65° C.for at least 5 minutes or to at least 90 to 93° C. for at least 1minute.

The compositions comprising an at least one olefin unsaturated estercopolymer and photoinitiator, crosslinking enhancer or combinationthereof preferably do not additionally contain another unsaturatedpolymer, particularly a polyene because the unreacted double bond inthese materials can adversely affect thermal stability of a tie layercomposition during melt processing. The unsaturated polymer might formgels detrimental to the physical and optical properties of a film.

In each instance, the composition comprising at least one olefinunsaturated ester copolymer and at least one photoinitiator ispreferably treated with sufficient actinic radiation, preferably UVlight to result in increased interlayer adhesion strength between twocomponents directly adjacent that composition as compared with theinterlayer adhesion strength before treatment with the actinic radiationand alternatively or in combination as compared with the adhesionstrength of a composition comprising the same base polymer or polymersbut without the compound or compounds selected from photoinitiators andcrosslinking enhancers either with or without irradiation. At least oneof the components preferably comprises a vinylidene chloride polymer. Inanother embodiment, at least one component exhibits interlayer adhesionstrength similar to vinylidene chloride polymers. Preferably the twocomponents with a tie layer of an olefin unsaturated ester copolymercomposition without a photoinitiator or crosslinking enhancer or withsuch compounds which have not been treated with sufficient actinicradiation to achieve enhanced interlayer adhesion strength haveinterlayer adhesion strength of less than 50 N/m, preferably less than40 N/m, more preferably less than 35 N/m, most preferably less than 30N/m, all measured at 93° C.

In each embodiment of the invention, at least one photoinitiator isadvantageously used in combination with at least one crosslinkingenhancer.

BRIEF DESCRIPTION OF THE DRAWINGS

Not applicable

DETAILED DESCRIPTION OF THE INVENTION

The following terms are used herein as defined below to aid indescribing the invention and in the claims.

“Multicomponent structure” means a structure having at least twoadjacent parts or components, often layers (which shall be used hereinas exemplary of the parts or components).

Adjacent components are affixed, that is for example bonded, welded,adhered or the like as contrasted with replaceably removable for examplea lid on a container. Examples of multicomponent structures includemultilayer films having at least two layers, laminated sheets having atleast two layers, composite packaging having at least two layers, moldedor shaped objects having at least two layers or shaped components bondedor adhered together. Preferred multicomponent structures includecoextruded articles such as film, tubing, laminates such as film andsheet, and injection and blow molded articles.

“Actinic radiation” refers to radiation that produces chemical change.Such irradiation generally involves relatively short wave lengths andincludes ultraviolet radiation, X-rays, and electron beam radiation. UVactinic radiation is used in the practice of the invention.

“Radiated” or “irradiated” means that the olefin unsaturated estercopolymer, shaped or in the form of an article or film, was subjected tothe source of UV actinic radiation sufficient to result in a chemicalchange, for example formation of a bond, or alternatively, having powerof at least 1 watt/(meter²) incident on the above article, whether ornot there is a measurable an increase in insoluble gel or otherindication of crosslinking.

“Ultraviolet” or “UV” means radiation at a wavelength or a plurality ofwavelengths in the range of from 150 to 700 nm which includes visiblelight, preferably 170 to 500 nm.

“Photoinitiator” means a chemical composition that, upon exposure toUV-radiation, generates radicals or species that can carry out hydrogenabstraction such as nitrenes, and carbenes without covalently bonding tothe main polymer chain.

“Crosslinking enhancer” in the practice of this invention means achemical composition that, in presence of a photoinitiator forms acovalent crosslink between two polymer chains. The crosslinking enhanceris also referred to herein as a photocrosslinker.

“Photoinitiator/crosslinker” means a chemical composition that uponexposure to UV-radiation generates a more reactive species (for example,free radical, carbene, and nitrene) that can form a covalent crosslinkbetween two polyolefin chains.

“Film” refers to a sheet, non-woven or woven web or the like orcombinations thereof, having length and breadth dimensions and havingtwo major surfaces with a thickness therebetween. A film can be amonolayer film (having only one layer) or a multilayer film (having twoor more layers). A multilayer film is composed of more than one layer(laminate, plies) preferably composed of at least two differentcompositions, advantageously extending substantially the length andbreadth dimensions of the film. Layers of a multilayer film are usuallybonded together by one or more of the following methods: coextrusion,extrusion coating, vapor deposition coating, solvent coating, emulsioncoating, or suspension coating. A film, in most instances, has athickness of up to 20 mils (5×10⁻⁴ m).

“Layer” or “ply” means herein a member or component forming all or afraction of the thickness of a structure wherein the component ispreferably substantially coextensive with the structure and has asubstantially uniform composition. In a monolayer film, the “film” and“layer” are one and the same.

“Extrusion,” and “extrude,” refer to the process of forming continuousshapes by forcing a molten plastic material through a die, followed bycooling or chemical hardening. Immediately prior to extrusion throughthe die, the relatively high-viscosity polymeric material is fed into arotating screw, which forces it through the die.

“Coextrusion,” and “coextrude,” refer to the process of extruding two ormore materials through a single die with two or more orifices arrangedso that the extrudates merge and weld together into a laminar structurebefore cooling or chilling, that is, quenching. Coextrusion is oftenemployed as an aspect of other processes, for instance, in film blowing,casting film, and extrusion coating processes.

“Crosslinked” or “crosslink” means the formation of chemical bondsdirectly or indirectly (via some chemical structural entity) between twoor more of the molecular chains of polymers. While degrees ofcrosslinking are typically shown by a change in the melt flow index, asmeasured according to ASTM D-1238, with respect to uncrosslinkedcomposition of the same type, or higher degrees of crosslinking aretypically reported as gel fraction as measured according to ASTM-D-2765,in the practice of this invention, crosslinking may not be measurable inthese ways. Crosslinking is believed to occur because a change occurs onexposure to UV radiation, which change seems consistent with lightcrosslinking. Use of the term crosslinking to describe this change isfor convenience and to facilitate description. Crosslinking is merelythe theorized explanation for increased interlayer adhesion. Theinvention is not limited changes in adhesion actually caused bycrosslinking.

“Substituted” as used herein means the result of a chemical reaction inwhich one atom or group of atoms replaces another atom or group of atomsin the structure of a molecule. It especially refers to the substitutionof a hydrogen atom, of a hydrogen-carbon moiety, with an alkyl, aryl,hydroxy, halogen, or other chemical substituent.

“Cook” means to heat a food product thereby effecting a change in one ormore of the physical or chemical properties thereof (for example, color,texture, and taste).

“Cook-in” as used herein is intended to refer to packaging structurallycapable of withstanding exposure to cook-in time-temperature conditionswhile containing a food product. Cook-in packaged foods are essentiallypre-packaged, pre-cooked foods that go directly to the consumer aconfiguration to be consumed with or without warming. Cook-intime-temperature conditions typically refer to a long slow cook, forexample submersion in water of at least 70° C. and preferably up to 80°C. for at least 4 hours, preferably up at least 6 hours, more preferablyup to 12 hours. Such cook-in time-temperature requirements arerepresentative of institutional cooking requirements. Under suchconditions, a cook-in packaging advantageously maintains seal integrityand is delamination resistant.

“Hot-fill” refers to processes wherein hot materials are packaged. Forinstance, hot foods may be packaged in bags. The hot materials arecommonly at temperatures of at least 65° C., preferably at least 85° C.Hot fill processes in most instances involve cooling immediately aftercontact with the hot materials or foods.

“Retorting” refers to exposure to temperatures of at least 100° C.,preferably at least 121° C., for a period of time sufficient to cook,pasteurize, sterilize or otherwise heat treat material.

“Elevated temperature” or “high temperatures” to which a multicomponentstructure of the invention may be exposed are those encountered inhot-fill, cook-in applications or retorting.

As a noun “laminate” refers to a multiple component structure having twoor more parts, preferably layers, sheets or films bonded together by anysuitable means, including adhesive bonding; reactive surfacemodification (for example, corona treatment, flame treatment, or plasmatreatment); heat treatment; and pressure treatment, includingcombinations thereof.

As a verb, “laminate” means to affix or adhere (by means of, forexample, adhesive bonding, pressure bonding, and corona lamination) twoor more separately made film articles to one another so as to form amultilayer structure; as a noun, “laminate” means a product produced bythe affixing or adhering just described.

“Delaminate,” and “delaminates” refer generally to the internalseparation of parts of a multicomponent structure, for example layers ofa film or laminate. More often the terms refer more specifically, to theseparation of a coextruded, multilayer film within a layer or at aninter-layer (that is, layer/layer) interface or both within thecoextruded film when such film, or laminate of which the coextruded filmis a component, is subjected to a peel force of sufficient magnitude.The terms “spontaneous delamination” and “spontaneously delaminate”refer to delamination without deliberate application of peeling force.Spontaneous delamination may occur, for Instance, in the course ofcommon commercial processing, for example hot fill or retort process ornormal handling thereafter.

“Peel,” and “peeling” refer generally to the act of removing one or morelayers from a multilayer film by manually or mechanically grasping andpulling back the layers along a plane or interface of relatively lowbond-strength or within a layer having relatively weak intra-layercohesion.

“Peel force” refers to the amount of force applied to ply-separate twolayers, or internally separate one layer or a combination thereof, of amultilayer film or laminate, as measured in accordance with ASTMF904-98.

“Adhesion strength” referred to as “peel-adhesion strength” and“interlayer adhesion strength” refer to the amount of force per arearequired to peel, delaminate or separate layers of a multilayer film, asmeasured according to the procedures of ASTM F904-98. For purposes ofthe present invention, measurement is at 93° C., unless statedotherwise.

“Bond-strength” refers generally to the adhesive force with which twoadjacent films, or two adjacent film layers, are connected.Bond-strength can be measured by the force required to separate twofilms or film layers that are connected, e.g., via a heat-weld, inaccordance with ASTM F88-94.

“Longitudinal direction” means that direction along the length of afilm, that is, in the direction of the film as it is formed duringextrusion, coating or both.

“Transverse direction” means that direction across the film andperpendicular to the machine direction.

“Directly adhered,” as applied to film layers, means adhesion of thesubject film layer to the object film layer, without a tie layer,adhesive, or other layer therebetween.

“Between,” as applied to film layers, means that the subject layer isdisposed in the midst of two object layers, regardless of whether thesubject layer is directly adhered to the object layers or whether thesubject layer is separated from the object layers by one or moreadditional layers.

“Oriented” or “stretch-oriented” refers to a polymer-containing materialwhich has been stretched at an elevated temperature (the orientationtemperature), followed by being “set” in the stretched configuration bycooling the material while substantially retaining the stretcheddimensions. A material can be stretched in one direction (uniaxialorientation), two directions (biaxial orientation), or multipledirections. Biaxial orientation typically occurs in two directions whichare perpendicular to one another, such as the longitudinal direction andthe transverse direction.

“Seal” (noun) means a bond of a first region of a film surface orcomponent surface to a second region of a film surface or componentsurface (or opposing surfaces). In heat sealing, it is created byheating (for example, by means of a heated bar, hot wire, hot air,infrared radiation, and ultrasonic sealing) the regions (or surfaces) toat least their respective softening points;

“Heat-seal” (also known as a “heat-weld”) refers to the union of twofilms by bringing the films into contact, or at least close proximity,with one another and then applying sufficient heat and pressure to apredetermined area (or areas) of the films to cause the contactingsurfaces of the films in the predetermined area to become molten andintermix with one another, thereby forming an essentially inseparablebond between the two films in the predetermined area when the heat andpressure are removed therefrom and the area is allowed to cool.

“Permeance” (in the packaging industry, “permeance” often is referred toas “transmission rate”) means the volume of a gas (for example, O₂) thatpasses through a given cross section of film (or layer of a film) at aparticular temperature and relative humidity when measured according toa standard test such as, for example, ASTM D 1434 or D 3985.

“Barrier layer” means a film layer with a low permeance toward one ormore gases (for example, oxygen, water vapor, odor, preferably oxygen).

“Inner layer” means a layer of a film having each of its principalsurfaces directly adhered to one other layer of the film.

“Outer layer” means a layer of a film having less than both of itsprincipal surfaces directly adhered to other layers of the film.

“Inside layer” means the outer layer of a film in which a product ispackaged that is closest, relative to the other layers of the film, tothe packaged product.

“Outside layer” means the outer layer of a film in which a product ispackaged that is farthest, relative to the other layers of the film,from the packaged product.

“Abuse layer” means an outer layer, an inner layer or both, that resistsabrasion, puncture, and other potential causes of reduction of packageintegrity, appearance quality or a combination thereof.

“Tie layer” or “adhesive layer” means an inner layer having a primarypurpose of providing interlayer adhesion to adjacent layers. The belayer may also impart other characteristics to the multicomponentstructure of which it is a part.

“Bulk layer” means any layer which has the purpose of increasing theabuse resistance, toughness, modulus, orientability, etc., of amulti-layer film and preferably comprises polymers that are inexpensiverelative to other polymers in the film.

“Seal layer” (or “sealing layer” or “heat seal layer” or “sealantlayer”) means the outer layer(s) involved in the sealing of the film toitself, another layer of the same or another film, another article whichis not a film or a combination thereof.

“Fabric substrate” is herein intended to be a general term encompassingany fabricated natural or synthetic material, whether woven, nonwoven,spunbonded, wet or dry laid, knitted, needled punched, felted, orotherwise constructed. For example, the fabric may be selected from thegroup consisting of nylon, cotton, polypropylene, PBI(polybenzimidazole), hemp, cellulose, silk, polyester, viscose, acrylic,acetate, flax, fiberglass, wool, polyethylene, aramid, rayon, jute,manila, NOMEX™ material, and blends thereof.

“Polymer” means the polymerization product of one or more monomers andis inclusive of homopolymers as well as interpolymers, copolymers,terpolymers, tetrapolymers, etc., and blends and modifications of any ofthe foregoing.

“Mer unit” means that portion of a polymer derived from a singlereactant molecule; for exam pie, a mer unit from ethylene has thegeneral formula —CH₂CH₂—.

“Homopolymer” means a polymer consisting essentially of a single type ofrepeating mer unit.

“Interpolymer” or “Copolymer” refers to a polymer that includes merunits derived from at least two reactants (normally monomers) and isinclusive of random, block, segmented, graft, etc., copolymers, as wellas terpolymers, and tetrapolymers. In this invention, the termscopolymer and interpolymer are used for polymers believed to be randomcopolymers unless stated otherwise.

“Olefin” refers to aliphatic (optionally branched), alicyclic andaromatic compounds having one or more double bonds. Representativeolefins include ethylene, propylene, 1-butene, 1-hexene, 1-octene,4-methyl-1-pentene, butadiene, cyclohexene, dicyclopentadiene, styrene,toluene, and α-methylstyrene. Aliphatic monounsaturated olefins arepreferred and have the general formula C_(n)H_(2n), such as ethylene,propylene, and butene.

“Polyolefin,” or “olefin polymer” means a thermoplastic polymer derivedfrom one or more olefins. The polyolefin can bear one or moresubstituents, for example, a functional group such as a carbonyl,sulfide, etc. In a polyolefin some mer units are derived from anolefinic monomer which can be linear, branched, cyclic, aliphatic,aromatic, substituted, or unsubstituted (for example, olefinhomopolymers, copolymers of two or more olefins, copolymers of an olefinand a non-olefinic comonomer such as a vinyl monomer). The term referspreferably to ethylene and propylene polymers and copolymers, and topolymeric materials having at least one aliphatic olefinic comonomer,such as ethylene vinyl acetate copolymer and ionomer. Polyolefins can belinear, branched, cyclic, aliphatic, aromatic, substituted, orunsubstituted. Included in the term polyolefin are homopolymers of anolefin, copolymers of olefins, copolymers of an olefin and anon-olefinic comonomer copolymerizable with the olefin, such as vinylmonomers, modified polymers of the foregoing. Modified polyolefinsinclude modified polymers prepared by copolymerizing the homopolymer ofthe olefin or copolymer thereof with an unsaturated carboxylic acid, forexample, maleic acid, fumaric acid or the like, or a derivative thereofsuch as the anhydride, ester metal salt or the like. They also includepolyolefins obtained by incorporating into the olefin homopolymer orcopolymer, an unsaturated carboxylic acid, for example, maleic acid,fumaric acid or the like, or a derivative thereof such as the anhydride,ester metal salt or the like.

“Ethylene/alpha-olefin copolymer” designates copolymers of ethylene withone or more comonomers selected from C₃ to C₂₀ alpha-olefins, such as1-butene, 1-pentene, 1-hexene, 1-octene, and methyl pentene. Includedare polymer molecules comprising long chains with relatively few sidechain branches obtained by low pressure polymerization processes and theside branching that is present is short compared to non-linearpolyethylenes (for example, LDPE, a low density polyethylenehomopolymer). Ethylene/alpha-olefin copolymers generally have a densityin the range of from 0.86 g/cc to 0.94 g/cc. The term linear low densitypolyethylene (LLDPE) is generally understood to include that group ofethylene/alpha-olefin copolymers which fall into the density range of0.915 to 0.94 g/cc. Sometimes linear polyethylene in the density rangefrom 0.926 to 0.94 is referred to as linear medium density polyethylene(LMDPE). Lower density ethylene/alpha-olefin copolymers may be referredto as very low density polyethylene (VLDPE, often used to refer to theethylene/butene copolymers available from Union Carbide Corporation witha density ranging from 0.88 to 0.91 g/cc) and ultra-low densitypolyethylene (ULDPE, typically used to refer to certain ethylene/octenecopolymers supplied by the Dow Chemical Company). Ethylene/alpha-olefincopolymers are the preferred polyolefins in the practice of theinvention.

The phrase “ethylene/alpha-olefin copolymer” also includes homogeneouspolymers such as metallocene-catalyzed EXACT™ linear homogeneousethylene/alpha-olefin copolymer resins commercially available from theExxon Chemical Company, of Baytown, Tex.; TAFMER™ linear homogeneousethylene/alpha-olefin copolymer resins commercially available from theMitsui Petrochemical Corporation; and long-chain branched,metallocene-catalyzed homogeneous ethylene/alpha-olefin copolymerscommercially available from The Dow Chemical Company, for instance,known as AFFINITY™ resins. The phrase “homogeneous polymer” refers topolymerization reaction products of relatively narrow molecular weightdistribution and relatively narrow composition distribution. Homogeneouspolymers are structurally different from heterogeneous polymers (forexample, ULDPE, VLDPE, LLDPE, and LMDPE) in that homogeneous polymersexhibit a relatively even sequencing of comonomers within a chain, amirroring of sequence distribution in all chains, and a similarity oflength of all chains, that is, a narrower molecular weight distribution.Furthermore, homogeneous polymers are most often prepared usingmetallocene, or other single-site type catalysts, rather than usingZiegler-Natta catalysts. Such single-site catalysts typically have onlyone type of catalytic site, which is believed to be the basis for thehomogeneity of the polymers resulting from the polymerization.

“(Meth)acrylic acid” means acrylic acid, methacrylic acid or acombination thereof.

“(Meth)acrylate” means acrylate, methacrylate or a combination thereof.

“Ethylene alkyl acrylate copolymer” (EAA) is used herein to define acopolymer formed from ethylene and alkyl acrylate comonomers wherein theethylene derived units in the copolymer are present in major amounts,and the alkyl groups include C₁-C₁₆ alkyl groups, preferably ethyl,methyl and butyl groups.

“Polyene” means a compound, possibly useful as a monomer, comprising anyunsaturated aliphatic or alicyclic compound containing at least fourcarbon atoms in a chain and having at least two carbon-carbon doublebonds in a carbon chain. While a polyene is optionally substituted, atleast two carbon-carbon double bonds in the compound are not separatedby a carbon-nitrogen or carbon-oxygen multiple bond or a heteroatom.Thus, while butadiene is a polyene, triallyl cyanurate and vinylacrylate are not.

LLDPE is an abbreviation for linear low density polyethylene and refersto copolymers of ethylene having: (1) a higher-alpha-olefin such asbutene, octene, hexene, etc. as a comonomer; (2) a density of from 0.910to as high as 0.935 grams per cubic centimeter; (3) molecules comprisinglong chains with few or no branches or cross-linked structures; and, (4)being produced at low to medium pressures by copolymerization usingheterogeneous catalysts based on transition metal compounds of variablevalance.

VLDPE is an abbreviation for very low density polyethylene and refers tocopolymers of ethylene having: (1) a greater proportion of higheralpha-olefin as a comonomer, in general, than LLDPE; (2) a density of0.910 to 0.86 or lower; (3) little low temperature embrittlement; and,(4) then produced by a catalytic, low pressure process at a pressure ofno greater than 7,000 KPA.

PVDC refers to copolymers of vinylidene chloride in which the vinylidenechloride monomer comprises at least 51 percent of the copolymer.Generally, PVDC is desirable as a layer in multi-layer thermoplasticfilm constructions because of its oxygen barrier properties.

EVA refers to copolymers of ethylene and vinyl acetate. The vinylacetate content may range from a low of 2 or 3 percent to a high of 40or 50 percent depending upon the desired properties.

EBA refers to ethylene/butyl-acrylate copolymer and the butyl-acrylatemonomer content varies from as low as 2 percent to 25 percent or higherby weight.

EMA refers to copolymers of ethylene and methyl acrylate. The vinylacetate content ranges from 2 or 3 percent to 30 or 40 percent dependingupon the desired properties.

EEA refers to copolymers of ethylene and ethyl acrylate. Typically, theethyl acrylate ranges from 2 to 3 percent to 20 to 25 percent dependingon the desired properties.

All percentages, preferred amounts or measurements, ranges and endpointsthereof herein are inclusive, that is, “less than 10” includes 10.

Vinylidene Chloride Polymer:

Multicomponent structures and multilayer films of the inventionpreferably have at least one component or layer comprising at least onevinylidene chloride polymer. The vinylidene chloride polymer or polymersadvantageously comprise a majority, preferably at least 51 weightpercent, more preferably at least 80, most preferably at least 90 weightpercent of the component or layer.

Vinylidene chloride polymers (also known as vinylidene chloride resins,interpolymers of vinylidene chloride, vinylidene chloride interpolymers,copolymers of vinylidene chloride, and PVDC) are well-known in the art.See, for example, U.S. Pat. Nos. 3,642,743 and 3,879,359. PVDC resinsknown as Saran™ resins, manufactured by The Dow Chemical Company arecommercially available, as are many other types of vinylidene chlorideinterpolymers such as PVDC resins supplied by Kureha Chemical IndustryCo. Ltd of Japan. As used herein, the term “interpolymer of vinylidenechloride,” vinylidene chloride interpolymer” or “PVDC” encompassescopolymers, terpolymers, and higher polymers wherein the major componentis vinylidene chloride and the remainder is one or moremono-ethylenically unsaturated monomer copolymerizable with thevinylidene chloride monomer such as vinyl chloride, alkyl acrylates,alkyl methacrylates, acrylic acid, methacrylic acid, itaconic acid,acrylonitrile, and methacrylonitrile. For use in the practice of theinvention, an interpolymer of vinylidene chloride and vinyl chloride orvinylidene chloride and an alkyl acrylate or alkyl methacrylate, ispreferred. The interpolymer optionally contains one or more otherunsaturated monomers as previously described, preferably in amounts lessthan the amount of vinyl chloride, alkyl acrylate or alkyl methacrylate(on a weight basis). Such interpolymers, especially those havingvinylidene chloride and vinyl chloride are suitable for mono-layer filmformation in a blown film process. In contrast, vinylidene chlorideinterpolymers not having vinyl chloride comonomers often have adjacentlayers of film for commercial film formation and are preferred forpractice of the invention.

Preferably, the vinylidene chloride interpolymer is formed from amonomer mixture comprising a vinylidene chloride monomer advantageouslyin an amount of at least 50, more advantageously at least 60, preferablyat least 75, more preferably at least 80, and most preferably at least90 weight percent, advantageously up to 99.9, preferably up to 98 weightpercent and the mono-ethylenically unsaturated comonomer in an amountadvantageously at least 0.1, preferably at least 3, more preferably atleast 5, most preferably at least 10 weight percent and advantageouslyup to 50, preferably less than or equal to 40, more preferably less thanor equal to 25 weight percent based on total weight of the vinylidenechloride interpolymer.

A variety of additives within the skill in the art are optionallyincorporated into the vinylidene chloride interpolymer composition.Additive type and amount will depend upon several factors. One suchfactor is the intended use of the composition. A second factor istolerance of the composition for the additives. That is, amount ofadditive that can be added before physical properties of the blends areadversely affected to an unacceptable level. Other factors are apparentto those skilled in the art of polymer formulation and compounding.

Exemplary additives include plasticizers, heat stabilizers, pigments,processing aids, lubricants, fillers, and antioxidants. Each of theseadditives is within the skill in the art and several types of each arecommercially available. Preferably, the vinylidene chloride polymercomposition contains only additives commonly used such as the listedtypes.

Exemplary lubricants include fatty acids, such as stearic acid; esters,such as fatty esters, wax esters, glycol esters, and fatty alcoholesters; fatty alcohols, such as n-stearyl alcohol; fatty amides, such asN,N′-ethylene bis stearamide; metallic salt of fatty acids, such ascalcium stearate, and magnesium stearate; and polyolefin waxes, such asparaffinic, and oxidized polyethylene. Paraffin and polyethylene waxesand their properties and synthesis are described in 24 Kirk-OthmerEncyc. Chem. Tech. 3rd Ed., Waxes, at 473-77 (J. Wiley & Sons 1980),which is incorporated herein by reference.

Additives are conveniently incorporated into the vinylidene chlorideinterpolymer composition using any mixing process that does not havesubstantial adverse effects on the interpolymer or additives, preferablydry blending techniques, alternatively melt blending or other meanswithin the skill in the art.

In a multilayer film a PVDC layer advantageously has a thickness atleast 2 microns (2×10⁻⁶ m), preferably at least 4 microns (4×10⁻⁶ m),more preferably at least 5 microns (5×10⁻⁶ nm) to achieve barrierproperties.

While a problem addressed by this invention generally concerns improvingthe adhesion of vinylidene chloride polymers, the invention isapplicable to other materials in a multicomponent structure that maydisplay less than desirable adhesion, especially under conditions ofelevated temperatures. It is particularly applicable to other materialsor combinations of materials that exhibit a peel or adhesion strengthsimilar to or less than that of the vinylidene chloride polymersadjacent to LLDPE. Advantageously, the two components with a tie layerof an olefin unsaturated ester copolymer composition (either without aphotoinitiator or crosslinking enhancer or with such compounds but nottreated with sufficient actinic radiation to achieve enhanced interlayeradhesion strength or both) have interlayer adhesion strength of lessthan 55, preferably less than 50, preferably less than 40, morepreferably less than 35, most preferably less than 30 N/m. Morespecifically, when the tie layer is the copolymer of an olefin and analkyl ester of an unsaturated acid, the interlayer adhesion isadvantageously less than 55, preferably less than 50, more preferablyless than 40 N/m. When the tie layer is a copolymer of an olefin and theester of an unsaturated alcohol and saturated acid, the adhesion isadvantageously less than 40, preferably less than 35, more preferablyless than 30, most preferably less than 25 N/m, all as measured at 93°C. While this invention has been exemplified in terms of vinylidenechloride polymers, it is similarly applicable, for instance, to otherpolymeric materials. These other polymers include halopolymers,polyolefins, polyesters, polyamides, polycarbonates, or a combinationthereof which also exhibit insufficient adhesion under certaincircumstances. Other halogen-containing polymers, referred to herein ashalopolymers such as poly(chlorotrifluoroethylene) homopolymers andcopolymers, ethylene chlorotrifluoroethylene copolymer, ethylenetetrafluoroethylene copolymer, fluorinated ethylene-propylene copolymer,perfluoroalkoxy polymer, poly(vinylidene fluoride), poly(vinylfluoride), poly(vinyl chloride), polychlorotrifluoroethylene (PCTFE),copolymers or blends of tetrafluoroethylene, copolymers or blends ofvinylidene chloride or fluoride, copolymers or blends of vinyl chlorideor fluoride, and blends of two or more of the foregoing, on occasionexhibit adhesion problems that are remedied by application of theinvention. Preferred halopolymers include preferably polyvinyl chloride(PVC) or polychlorotrifluoroethylene (PCTFE) as well as the copolymersof vinylidene chloride previously described and referred to herein aspolyvinylidene chloride or PVDC and combinations thereof.

Polyolefin Unsaturated Ester Polymer

In the practice of the invention, the interlayer adhesion of componentsis increased using a composition comprising at least one olefinunsaturated ester copolymer and at least one photoinitiator, optionallywith at least one crosslinking enhancer.

The olefin unsaturated ester copolymer is a copolymer or interpolymercomprising at least one olefin monomer and at least one monomer which isan ester and has unsaturation, preferably at least one double bondinterpolymerizable with the olefin monomer or monomers. The ester ispreferably a carboxylic acid ester and is referred to herein as anunsaturated ester. Either the acid moiety or the alcohol moiety of theester is optionally unsaturated, or both. Examples of unsaturated esterswherein the acid moiety is unsaturated include acrylates andmethacrylates. These esters are preferably alkyl esters such as methylacrylate, ethyl acrylate, and butyl acrylate. Examples of unsaturatedesters wherein the alcohol moiety is unsaturated include vinyl esters,such as vinyl acetate as well as vinyl propionate, vinyl butyrate, vinylhexanoate.

Copolymers of olefins and alkyl esters of unsaturated carboxylic acidsare known in the art and commercially available such as the ethylenemethyl acrylate copolymers and ethylene butyl acrylate copolymerscommercially available from Eastman Chemical Company under the tradedesignations EMAC, EMAC+, EBAC and EBAC+ with numeric designationsbeginning with the letters SP, such as SP 2255, SP2258, SP2205, SP1400,SP 1307, and SP 1903, copolymers of ethylene and methyl acrylatecommercially available from Gulf Oil and Chemicals Co. under the tradedesignation POLY-ETH 2205 EMA, ethylene ethyl acrylate (EEA)commercially available from The Dow Chemical Company under tradedesignations such as EA 100, EA 101, and EA 103, and ethylenemethacrylic acid ionomers commercially available from DuPont under thetrade designation SURYLN; ethylene/acrylic acid copolymers; and maleicanhydride modified polyolefins and copolymers of polyolefins,commercially available from Mitsubishi Chemical Company under the tradedesignation MODIC resins. Preferred olefins are alpha olefins, that is,ethylenically unsaturated compounds having a single double bond in thealpha or first position. Of the alpha olefins, preferably C₂-C₂₀, morepreferably C₂-C₁₀ alpha olefins; ethylene is most preferred; otherpreferred alpha olefins include propylene, 1-butene, 1-pentene,1-hexene, 1-heptene, and 1-octene. Among effective alkyl esters ofunsaturated carboxylic acids, the alkyl esters of acrylic andmethacrylic acid are preferred, with acrylates more preferred. Of thealkyl esters, straight chain alkyl groups are preferred, with sizes ofC₁ to C₂₀ preferred, C₁ to C₄ alkyl groups more preferred, and methyl,ethyl, or butyl groups most preferred, and ethyl or methyl groups evenmore preferred, in each instance inclusive of combinations thereof. Thecopolymers are optionally, but not preferably, terpolymers or higherpolymers, having up to 30, advantageously less than 20, preferably lessthan 10, more preferably less than 5, most preferably less than 3 weightpercent of at least one other ethylenically unsaturated monomerinterpolymerized therewith. These optional monomers include styrene,acrylonitrile, methyl methacrylate, acrylic acid, methacrylic acid, andvinyl acetate. Methyl acrylate is the most preferred alkyl ester. Thecopolymer advantageously has at least 1, more preferably at least 20weight percent alkyl ester based on total weight of the copolymer ofolefin and alkyl ester of unsaturated carboxylic acid. While up to 50weight percent or more alkyl ester is useful, more preferably less thanor equal to 40, most preferably less than 30 weight percent alkyl esteris present in the copolymer to achieve desired bond or adhesionstrength.

Copolymers of olefins and carboxylic acid esters of unsaturated alcoholmoieties are known in the art and commercially available such as theethylene vinyl acetate copolymers commercially available from DuPontunder the trade designation ELVAX series and commercially available fromQuantum Chemical Corp. under the trade designation ULTRATHENE series andthe carboxylated ethylene/vinyl acetate copolymers, commerciallyavailable from DuPont under trade designations such as CXA 3101.Preferred olefins are alpha olefins, that is, ethylenically unsaturatedcompounds having a single double bond in the alpha or first position. Ofthe alpha olefins, preferably C₂-C₂₀, more preferably C₂-C₁₀ alphaolefins; ethylene is most preferred; other alpha olefins includepropylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. Amongeffective carboxylic acid esters of unsaturated alcohols, the esters ofC₂-C₂₀ carboxylic acids are preferred, with acetates and butyrates morepreferred. Of the unsaturated esters, straight chain unsaturated groupsare preferred, with sizes of C₃ to C₂₀ preferred, C₃ to C₄ groups morepreferred and vinyl groups most preferred. Examples include vinylacetate, vinyl propionate, and vinyl hexanoate. The copolymers areoptionally, but not preferably, terpolymers or higher polymers, havingup to 30, advantageously less than 20, preferably less than 10, morepreferably less than 5, most preferably less than 3 weight percent of atleast one other ethylenically unsaturated monomer interpolymerizedtherewith. These optional monomers include styrene, acrylonitrile,methyl methacrylate, acrylic acid, methacrylic acid, and vinyl acetate.Methyl and ethyl acrylates are the most preferred alkyl esters. Thecopolymer advantageously has at least 1, more preferably at least 10weight percent unsaturated ester based on total weight of the copolymerof olefin and unsaturated ester of unsaturated carboxylic acid. While upto 50 weight percent or more alkyl ester is useful, more preferably lessthan or equal to 40, most preferably less than 30 weight percent alkylester is present in the copolymer to achieve desired bond or adhesionstrength.

The preferred olefin unsaturated acid copolymer having unsaturatedalcohol moiety is ethylene vinyl acetate (EVA). Preferred EVA's arethose having a higher vinyl acetate (VA) content, typically greater than12 weight percent. EVA'S having higher VA content tend to yield EVAlayers having increased adhesion to for example, the vinylidene chloridecopolymer layer. Thus, higher VA contents, in the range of at least 12percent, preferably at least 18, percent (by weight) vinyl acetate arepreferred. The vinyl acetate content is advantageously less than orequal to 40 weight percent. A melt index of less than 6 is alsopreferred.

The olefin unsaturated ester copolymers are optionally, but notpreferably, modified by introduction of adhesive functional groups suchas maleic anhydride, hydroxyl functionality, and alkoxy silanefunctionality. Examples of modified olefin unsaturated ester copolymersinclude maleic an hydride-modified EVA commercially available fromDuPont under the trade designation Bynel, glycidyl functionally-modifiedEVA commercially available from DuPont under the trade designationElvaloy, glycidyl-modified ethylene acrylate polymers commerciallyavailable from Atofina under the trade designation Lotader, andexperimental alkoxyl-silane modified ethylene methyl acrylate resinscommercially available from DuPont under the trade designation Elvaloy.

Blends of the unsaturated ester copolymers are also suitable for use inthe practice of the invention. Useful bends include those of polymershaving different monomer identities, as well as those having the samemonomers in different proportions or having differences in at least onecharacteristic such as molecular weight, melt index, or other property.Any of the unsaturated ester copolymers are optionally used when blendedwith another unsaturated ester copolymer in any compatible proportion.For instance, blends of EVA and at least one of EMA, EEA, EBA or anotherEVA of different composition, molecular weight, melt index or otherproperty are effective in the practice of the invention. Ratios aredetermined without undue experimentation by those skilled in the art,which artisans recognize that compatibility and effectiveness in eachparticular application considering such factors as adjacent layers,other purposes the layers may serve and conditions to which the layersare exposed. For instance equal portions of the blended polymers areamong the effective blends. Similarly, the unsaturated ester copolymersare optionally blended with polymers which are not unsaturated estercopolymers. In such blends an additional important factor is theconcentration of unsaturated ester, for example acrylate or vinylacetate. The amounts of unsaturated ester in the blend are preferablythose amounts preferred in each unsaturated ester when used alone. Forinstance, where EVA, EEA or EMA used alone preferably contains at least12 percent by weight vinyl acetate or acrylate ester, a blend of one ormore of those polymers with a polymer not containing unsaturated esterwould preferably contain 12 percent by weight vinyl acetate or acrylateester, obtained, for instance, blending a unsaturated ester copolymercontaining a higher weight percent unsaturated ester with the otherpolymer. For instance, 33 weight percent polyethylene, for example LDPE,can be blended with 67 weight percent EVA containing 18 weight percentvinyl acetate to obtain a blend having 12 weight percent vinyl acetate.

In one preferred embodiment the tie layer includes at least two olefinunsaturated ester copolymers having different molecular weights,referred to herein as a higher and a lower molecular weight, althoughmore than two such copolymers of differing molecular weights areoptionally present and each molecular weight often, in reality,represents a collection of molecular weights. The different polymers arepreferably compatible, and more preferably either both olefinunsaturated acid copolymers or both olefin carboxylic acid esters ofunsaturated alcohol copolymers, preferably both olefin unsaturated acidcopolymers, most preferably both selected from EMA, EBA and EEAcopolymers. For convenience, rather than refer to a measured molecularweight, the melt index determined according to the procedures of ASTMD-1238 using a temperature of 190° C. and a weight of 2.16 kg is used toindicate relative molecular weights. At least among similar polymers, apolymer with a higher melt index (MI, also referred to as I₂) isunderstood by those skilled in the art to have a lower molecular weight.The polymer of highest molecular weight, lowest melt index, isadvantageously sufficient to increase chain entanglement, crosslinking,or both preferably having a melt index of less than 2 g/10 min, morepreferably less than 1 g/10 min, most preferably less than 0.6 g/10 min,and advantageously is not of sufficiently high molecular weight topresent difficulties in melting the polymer blend at temperaturesfrequently encountered in making multicomponent structures andparticularly at temperatures deleterious to vinylidene chloride polymersas used in the practice of the invention, preferably having a melt indexgreater than 0.1 g/10 min, more preferably greater than 0.3 g/10 min.The lowest molecular weight polymer, having highest melt index, isadvantageously of sufficiently low molecular weight to provide goodcoextrusion flow with the other polymer layers, preferably having a meltindex of less than 10 g/10 min, more preferably less than 6 g/10 min,most preferably less than 3 g/10 min, and is less than the molecularweight of the highest molecular weight component, advantageously havinga melt index of at least 0.5 g/10 min, preferably at least 1.5 g/10 min,more preferably at least 1.0 g/10 min and most preferably at least 2.0g/10 min. The highest and lowest molecular weights preferably differ inmelt index by at least 1 g/10 min, more preferably at least 2 g/10 min,preferably less than 8 g/10 min, more preferably by less than 6 g/10min, and most preferably by less than 4 g/10 min. The components ofdiffering molecular weights advantageously are combined in amounts whichprovide improved adhesion compared to the high melt index fractionalone, but can still be successfully coextruded without flow problemsexperienced with the low melt index fraction alone. The highestmolecular weight polymer (lowest melt index) is advantageously presentin an amount of at least 10 weight percent, preferably at least 20weight percent, more preferably at least 30 weight percent, andadvantageously less than 60 weight percent, preferably less than 50weight percent, more preferably less than 40 weight percent of thecombination of unsaturated ester copolymers. These copolymer blends arebelieved to result in an improved adhesion strength as compared with thelower molecular weight component alone and improved processing ascompared with the higher molecular weight component alone, preferablyimproved adhesion strength as compared with either (or any) componentalone even when used without the photoinitiator and, optionally,crosslinking enhancer as taught herein.

Advantageously, the olefin unsaturated ester copolymer is selected forits processability, that is ease of extrusion under conditions commonlyused in the industry and width of temperature window in which extrusioncan take place. Its melt processability is enhanced by using copolymersof an olefin and alkyl ester of an unsaturated carboxylic acid having amelt index (in the case of a mixture of unsaturated ester copolymers asimple arithmetic average of melt indexes) of at least 0.1, preferably0.5, more preferably at least 1, and advantageously less than 500,preferably less than 10, more preferably less than 6, most preferably 2,for example in the range of 1.5 to 2.5 g/10 min. Melt index isdetermined according to the procedures of ASTM D-1238 using atemperature of 190° C. and a weight of 2.16 kg.

The thickness of an olefin unsaturated ester layer is advantageously atleast 2, preferably at least 3, more preferably at least 5, and mostpreferably at least 7 percent, advantageously up to 50, preferably to30, more preferably to 20, still more preferably to 15, and mostpreferably to 10 percent (inclusive), of the total thickness of themultilayer film. Each bonding layer may have a thickness in the range offrom 1 to 15 microns, and is preferably selected from the groupconsisting of ethylene vinyl acetate, ethylene methyl acrylate, ethyleneethyl acrylate, ethylene butyl acrylate, and combinations thereof.

The olefin unsaturated ester copolymers are optionally used withadditives within the state of the art. Those skilled in the art willrecognize that some such additives could interfere with the practice ofthe invention especially if used in large amounts. The identities andamounts that might interfere differ with the identities and amounts ofthe polymers, photoinitiators and cross-linking enhancers used.Determining interference and avoiding it is within the skill in the artwithout undue experimentation. Significant interference is preferablyavoided.

Photoinitiators

The compositions involved in the present invention include one or morephotoinitiators, and the compositions optionally also include one ormore crosslinking enhancers.

Examples of useful photoinitiators include aromatic ketones, aromaticmonoacetals of 1,2-diketones, aromatic α-hydroxy ketones, quinones,organic peroxides, azo compounds, nitroso compounds, acyl halides,hydrazones, mercapto compounds, pyrylium compounds, triacylimidazoles,acylphosphine oxides, bisimidazoles, chloroalkyltriazines, benzoinethers, benzil ketals, thioxanthones, and mixtures thereof.

The preferred photoinitiators used in the practice of the invention arearomatic ketones or monoacetals of 1,2-diketones. There are twomechanisms of photoinitiation with these photoinitiators. In the case ofaromatic ketones, where the carbonyl functionality is linked to one ortwo aromatic groups, the carbonyl group is upon exposure to UV radiationexcited into a triplet state. Such excited carbonyl group can abstract ahydrogen atom from a polymer chain and generate a radical site on apolymer. Recombination of free radicals from separate polymer chains isbelieved to result in a covalent crosslinking. On the other hand, theprimary photoreaction of the monacetals is believed to be homolytic bondcleavage to give acyl and dialkoxyalkyl or dialkoxyaryl radicals knownas a Norrish Type I reaction. Those mechanisms of photoinitiation aremore fully described in W. Horspool and D. Armesto, OrganicPhotochemistry: A Comprehensive Treatment, Ellis Horwood Limited,Chichester, England, 1992; J. Kopecky, Organic Photochemistry: A VisualApproach, VCH Publishers, Inc., New York, N.Y. 1992; N. J. Turro, etal., Acc. Chem. Res., 1972, 5, 92; and J. T. Banks, et al., J. Am. Chem.Soc., 1993, 115, 2473. The synthesis of monoacetals of aromatic 1,2diketones, Ar—CO—C(OR)₂—Ar′ is described in U.S. Pat. No. 4,190,602 andGer. Offen. U.S. Pat. No. 2,337,813.

The preferred compounds from the class of aromatic ketones include, butare not limited to, benzophenone, 4-methylbenzophenone,4-aminobenzophenone, 4-methoxybenzophenone, 4-morpholinobenzophenone,dimethylbenzophenone, dimethoxybenzophenone, diphenoxybenzophenone,4,4′-bis(dimethylamino)-benzophenone, acetophenone,p-methylacetophenone, p-methoxyacetophenone, butyrophenone,α-phenyl-butyrophenone, valerophenone, 1′-acetonaphthone,2′-acetonaphthone, 1-hydroxycyclohexyl phenyl ketone,2-hydroxy-2-methyl-1-phenylpropane-1-one, p-morpholinopropiophenone,2-hydroxy-2-phenylacetophenone (benzoin), benzoin methyl ether, benzointetrahydrophyranyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone,p-diacetylbenzene, 1,3,5-triacetylbenzene, anthrone, anthraquinone,acenaphthenequinone, 2-acetylphenanthrene, 3-acetylphenanthrene,9-acetylphenanthrene, 7H-benz[de]anthracen-7-one,benz[a]anthracene-7,12-dione, 9-fluorenone, α-tetralone,dibenzosuberone, xanthone, xanthene-9-one, isopropylthioxanthone,thioxanthen-9-one, thioxanthen-10-one, 1-indanone and benzyl. The morepreferred photoinitiators from this class are benzophenone, anthrone,xanthone, and their alkyl- or acyl-substituted derivatives like4-methylbenzophenone, 2-hydroxy-2-phenylacetophenone (benzoin),2-hydroxy-2-methyl-1-phenyl-1-propanone, and 1-hydroxycylcohexyl phenylketone, with benzophenone being the most preferred.

The preferred compound from the class of monoacetals of aromatic 1,2diketones is 2,2-dimethoxy-2-phenylacetophenone which is commerciallyavailable from Ciba-Geigy as Irgacure 651.

Preferred photoinitiators have low migration from the formulated resin,as well as a low vapor pressure at extrusion temperatures and sufficientsolubility in the polymer or polymer blends to yield good crosslinkingefficiency. The vapor pressure and solubility, or polymer compatibility,of many familiar photoinitiators can be easily improved if thephotoinitiator is derivatized. The derivatized photoinitiators include,for example, higher molecular weight derivatives of benzophenone, suchas 4-phenylbenzophenone, 4-allyloxybenzophenone, and4-dodecyloxybenzophenone. In one embodiment, the photoinitiator isoptionally covalently bonded to a polymer or to a polymer diluent, suchas described in U.S. Pat. No. 5,993,922. In one embodiment, preferredphotoinitiators are substantially non-migratory from the multicomponentstructure.

The photoinitiators are advantageously used in an effective amount, thatis an amount effective to increase the adhesion strength as measured at93° C. between two layers or components having directly therebetween acomposition comprising at least one olefin unsaturated ester copolymer,the photoinitiator and optionally at least one crosslinking enhancerafter treatment with an effective amount of UV radiation at an effectivewavelength. The amount of photoinitiator is advantageously sufficient toincrease the adhesion strength after treatment with UV radiation fromthat measured without photoinitiator or radiation. The differencebetween adhesion strengths of with and without use of the composition ofolefin unsaturated ester copolymer and irradiation used in the practiceof the invention is advantageously at least 20, more advantageously atleast 30, most advantageously at least 40, preferably at least 50, morepreferably at least 75, and most preferably at least 100 N/m.Alternatively the increase in adhesion strength is advantageously atleast 30, more advantageously at least 40, most advantageously at least50, preferably at least 75, more preferably at least 100, mostpreferably at least 150 percent.

Effective amounts are advantageously amounts of at least 100 parts permillion (ppm), more advantageously at least 500 ppm, most advantageouslyat least 0.10 percent, more preferably at least 0.2 weight percent. Theamount of photoinitiator is advantageously less than or equal to 10weight percent, preferably less than or equal to 4 weight percent, morepreferably less than or equal to 2 weight percent. The most preferredamount of photoinitiator depends on the actual application. Higherlevels of photoinitiator (at least 1 weight percent and less than orequal to 2 weight percent) are believed to increase the crosslinkdensity of the cured composition. In applications such as foodapplications where there may be concern regarding the possibility ofcertain photoinitiators contacting food or otherwise not remainingconfined to the tie layer or other layers not in contact with the foodor other substance where contact would not be preferred, lowest levelsof photoinitiator consistent with sufficient adhesion are preferred,that is less than 1 percent is advantageous, less than 0.5 percent moreadvantageous, less than 0.1 percent (all inclusive). Otherwise, sortieother means of avoiding contact such as a barrier to migration of thephotoinitiator, crosslinking enhancer, or both is preferred.

Crosslinking Enhancers

In one embodiment of the invention, the photoinitiator is used incombination with a crosslinking enhancer also referred to as aphotocrosslinker. Any photocrosslinker that will upon the generation offree radicals or species that carry out hydrogen abstraction such asnitrenes, and carbenes link two or more polymer backbones togetherthrough the formation of covalent bonds with the backbones can be usedin this invention. Preferably these photocrosslinkers arepolyfunctional, that is, they comprise two or more sites capable offorming a covalent bond with a site on the backbone of the polymer.Representative photocrosslinkers include, but are not limited to,polyfunctional vinyl or allyl compounds, including multifunctionalacrylates and methacrylates. Typical multifunctional acrylates andmethacrylates have molecular weights of 150 to 1,000 and contain atleast two polymerizable unsaturated groups per molecule. The preferredphotocrosslinkers include, but are not limited to, triallyl cyanurate,triallyl isocyanurate, pentaerythritol triallyl ether, pentaerythritoltriacrylate, pentaerythritol tetraacrylate, pentaerythritoltetramethacrylate, dipentaerythritol pentaacrylate, ethylene glycoldiacrylate, ethylene glycol dimethacrylate, tetraethylene glycoldiacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate,1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate,methoxy-1,6-hexanediolpentaerythritol triacrylate, trimethylolpropanetriacrylate, trimethylolpropane trimethacrylate, diallyl maleate,dipropargyl maleate, dipropargyl monoallyl cyanurate, polymethacrylateurethanes, polymeric epoxy acrylates, polyester acrylate monomers andoligomers, poly-n-butyleneoxide glycol diacrylates, and bisphenol Aalkylene oxide adduct diacrylates and combinations thereof. Particularlypreferred photocrosslinkers are triallycyanurate, triallylisocyanurate,pentaerythritol triallyl ether, pentaerythritol tetraacrylate,trimethylolpropane triacrylate, and trimethylolpropane trimethacrylatewhich are all commercially available.

In general, difunctional photocrosslinkers are less efficient than theiranalogues having higher level of functionalities. In compositionscontaining photocrosslinkers with higher level of functionalities, thecompression set, gel formation or other indicator of crosslink densityare enhanced compared to compositions containing difunctionalphotocrosslinkers. Consequently, photocrosslinkers of the class havinghigher functionalities are preferred for purposes of the presentinvention.

Certain compounds act as both a photoinitiator and a photocrosslinker inthe practice of this invention. These compounds are characterized by theability to generate two or more reactive species (for example, freeradicals, carbenes, and nitrenes) upon exposure to UV-light and tosubsequently covalently bond with two polymer chains. Any compound thatcan perform these two functions can be used in the practice of thisinvention. Representative compounds include the sulfonyl azidesdescribed in U.S. Pat. Nos. 6,211,302 and 6,284,842, which areincorporated herein by reference for their description of sulfonylazides. Since such compounds function as photoinitiators, the termphotoinitiator as used herein encompasses these compounds. Similarly,they are included in the term crosslinking enhancers. As such, they areoptionally used in combination with other photoinitiators, crosslinkingenhancers or both.

Use of crosslinking enhancers is optional. Crosslinking enhancers arepreferably used when the desired level of crosslinking exceeds thatconveniently obtainable using a desired concentration of photoinitiator.This can occur, for instance, when the olefin unsaturated estercopolymer is less facilely crosslinked, a high degree of crosslinking isdesired, the activity or desired concentration of photoinitiator isrelatively low or a combination of factors.

Crosslinking enhancers are used in and effective amount, that is anamount which improves the adhesion strength for a given photoinitiatorconcentration. Such amounts are advantageously at least 0.001,preferably at least 0.01, more preferably at least 0.1, most preferablyat least 0.2 weight percent. Preferably the crosslinking enhancers areused in amounts less than that which would cause excessive crosslinkingor adversely affect such qualities as thermal stability duringprocessing. Such amounts are advantageously less than 5, preferably lessthan 4, more preferably less than 3, most preferably less than 2 weightpercent.

The compositions involved in the present invention can also include oneor more compounds that can act as antioxidants, light stabilizers orcombinations thereof in the polymer photocrosslinking. The preferredantioxidants are chosen from the class of hindered phenols, an exampleincludes, but is not limited to, Irganox 1076 which is Octadecyl3-(3′,5′-di-tert-4′-hydroxyphenyl) propanoate commercially availablefrom Ciba Geigy Corp.). The preferred light stabilizers are hinderedamines (hindered amine light stabilizers, or HALS). An example includes,but is not limited to, Tinuvin 770 which isbis(2,2,6,6-Tetramethyl-4-piperidinyl) sebacate commercially availablefrom Ciba Geigy Corp.

The olefin unsaturated ester copolymer and a photoinitiator (andoptionally a photocrosslinker, photoadditives or a combination thereofare suitably mixed at any time and by any means within the skill in theart. They are advantageously mixed during the film-forming extrusionstep, for instance, by using a single or twin screw extruder in any ofvarious mixing sections in manners within the skill in the art. Forinstance one or more of the photoinitiators, crosslinking enhancers andphotoadditives, in solid or liquid form with or without diluents, areadmixed with the polymer, for example in pellet or powder form andintroduced into equipment which includes one or more extruders. In someinstances, it may be preferable to pre-compound photoadditive(s) priorto the extrusion step. In such approach, the photoadditive(s) areadvantageously introduced for example using a masterbatch concentratecomprising the same or different base resin as the polyolefinunsaturated ester polymer. Preferably, the photoadditive concentrationfor the masterbatch ranges from 2 to 25 weight percent (based on thetotal weight of the concentrate).

Actinic Radiation

UV actinic radiation is provided to the composition comprising at leastone olefin unsaturated ester copolymer and at least one photoinitiatorsufficient to achieve an increase in interlayer or inter-componentadhesion. For purposes of the process of this invention, the wavelengthspectrum of radiation advantageously corresponds to the absorptionmaximum of a photoinitiator or crosslinking enhancer that is activatedby radiation. Irradiation can be done by any conventional means. In theirradiation process, preferably the multicomponent structure ormultilayer film is subjected to UV radiation treatment, which isbelieved to induce crosslinking between molecules of the irradiatedmaterial. While the invention is conveniently explained in terms ofcrosslinking, it should not be limited to this scientific theory of themechanism of increasing adhesion.

In the case of most of the preferred photoinitiators and crosslinkingenhancers, the absorption maximum ranges are usually from 170,preferably from 200, to 700 nanometers, preferably to 500 nanometers.This range is generally in the UV spectrum. Suitable UV radiationsources include medium pressure mercury vapor lamps, electrodelesslamps, pulsed xenon lamps, and hybrid xenon/mercury vapor lamps. Apreferred arrangement comprises one or more lamps together with areflector, which diffuses the radiation evenly over the surface to beirradiated. When the invention involves treatment of multilayer film ina process including extrusion through a die, a UV source capable ofincreasing the adhesion of the tie layer composition according to thepractice of the invention is conveniently positioned near the die toirradiate the film in a molten state. Alternatively, the UV source isadvantageously positioned to irradiate the film later, for instanceafter it has been quenched, during subsequent film handling steps. Thisstep is optionally part of the conventional film fabrication processes,or a separate step to increase the adhesion of at least one tie layeraccording to the practice of the invention.

The radiation dosage is an effective amount, that is, sufficient toincrease the inter-component or interlayer adhesion, believed to be theresult of crosslinking in the composition. The amounts of increase areadvantageously those previously described. Preferably, the dosage issufficient to achieve maximum interlayer adhesion, which can bedetermined by those skilled in the art by testing a series of dosagesuntil increased dosage does not increase the adhesion. The dosage,including power of the electromagnetic radiation and the irradiationtime, is chosen to allow efficient adhesion improvement withoutunacceptable levels of polymer degradation, dimensional defects or acombination thereof. The dosage advantageous for a particularapplication will depend on such factors as the configuration of thecomponent or layer in the structure or film, the composition of thelayers and additives, the temperature of the material being irradiatedand the particular wavelength used. Determining the dosage required forimproved adhesion for any particular set of conditions is within theskill in the art.

A dosage of at least 1 joule per square meter, preferably at least10,000 J/m² more preferably at least 100,000 J/m² is sufficient in mostinstances. In some compositions, an excessive dosage may result in somecolor of one or more components or layers of a multicomponent structure.Undesirable levels of such color are preferably avoided by reducing thedosage to until acceptable color is obtained, for instance to less than5,000,000 J/m². Dosage is the source intensity (or power) (in watts)multiplied by the exposure time (in seconds) divided by the area oftreated film (square meters). Area treated is a function of the sourceand the distance from the UV radiation source. In most instances, anacceptable degree of treatment can be obtained by exposures of at least0.1 seconds, more advantageously at least 0.5, preferably at least 0.75,more preferably at least 1, most preferably at least 1.5 seconds. Theexposure is advantageously less than or equal to 30 seconds, moreadvantageously less than or equal to 15, preferably less than or equalto 10, more preferably less than or equal to 5, most preferably lessthan or equal to 2 seconds using a lamp or other source of 4,800 W, over0.0155 meter² of treated film corresponding to a UV exposure intensityof 310,000 J/m². 0.1 to 5 seconds corresponds to exposure tocommercially available light sources at a convenient line speed formaking and processing multilayer film. Appropriate adjustments for powerof the lamp, distribution of the output over the UV range, the thicknessof the sample as well as the polymeric component, and level ofphotoinitiator and crosslinking enhancer present are within the skill inthe art.

The irradiation source is advantageously any UV-light generatoroperating in a range of 50 watts to 25,000 watts with a power outputcapable of supplying the desired dosage. Adjusting wattage to levelsappropriate for a particular multicomponent structure or film and theequipment used for it is within the skill in the art. Irradiation isconveniently carried out at room temperature, although othertemperatures are well within the practice of the invention.Photoinitiated processes are usually faster at higher temperatures.Preferably, the irradiation is carried out after shaping or fabricationof the structure or film.

In a preferred embodiment, at least one photoinitiator, optionally withat least one crosslinking enhancer, other photoactive additive or acombination thereof with sufficient thermal stability is admixed with apolyolefin unsaturated ester resin, formed into a film or structure, andirradiated in a continuous process using one energy source or severalunits linked in a series.

Advantages to using a continuous process compared with a batch processto cure a film or sheet include reduced handing and equipmentrequirements.

In another embodiment of the invention, the component or layer need notbe treated upon extrusion, but may be irradiated at some late r time, atthe convenience of the processor, and typically in conjunction withother processing steps. In this embodiment, treatment optionally takesplace at room temperature or at an elevated temperature below themelting point of the structure or film as a whole. For example, a filmhaving layers with different melting points can be heated to atemperature between the melting points and then irradiated. The effectof treatment is expected to be enhanced in the layer with the lowermelting point.

The present invention as described herein relates especially to improvedmethods and materials for making multilayer thermoplastic films,however, one of ordinary skill in the art will readily recognize that itis applicable to thermoplastic objects in a variety of forms such ascups, bottles, trays and other packaging. In addition, a film or layeraccording to the present invention is optionally used with a variety ofsubstrates, including other polymeric materials, paper, glass, silica,and metal, as well as fabrics made from natural and synthetic fibers.

A multilayer plastic film in accordance with the invention can beproduced by methods such as coextrusion, lamination, extrusion coating,corona bonding, blowing film, casting film, and extrusion coatinglamination, preferably by coextrusion, more preferably by a combinationof coextrusion and blowing or coextrusion and casting. A multilayerplastic film or multicomponent structure in accordance with theinvention ca n also be used to produce bottles and other containers byblow molding or other processes within the skill in the art. Suchmethods are well within the skill in the art.

The films are conveniently made by blown film process within the skillin the art. Blown film extrusion processes are known and are described,for example, in U.S. Pat. Nos. 2,409,521, 2,476,140, 2,634,459,3,750,948, 4,997,616, 5,213,725, and 5,700,489. In an exemplary blownfilm extrusion process, commonly known as the “double bubble” process, amolten thermoplastic polymer is extruded through a tubular die. Theextruded molten polymer exits the die and is quenched in a cold waterbath into an amorphous polymer tube. This amorphous polymer tube iscollapsed into a tape and then passed through a second warm water tankfor conditioning prior to being formed into a bubble or blown film bythe pressure of internal air in a bubble. The blown film is collapsedinto a flat web, which is optionally split to form two layers of film.

In a preferred multilayer film embodiment, the film has orientationinsufficient to provide shrink properties, preferably less than 5percent shrink in both directions measured at 100° C. These films areeither produced by a cast process or by a conventional blown filmprocess where the molten polymer exits the die and is cooled by an airring.

Alternatively, a multi-layer barrier film of the invention may beproduced by lamination technique using an appropriate adhesive layer.For example, it is possible that the barrier layer and a skin layer(single layer or plural layers) are separately formed and then they arelaminated together using an composition comprising at least one olefinunsaturated ester copolymer and at least one photoinitiator.

One technique for manufacturing multilayer films of the presentinvention can use a coextrusion technique, such as that described inInternational Publication No. WO 93/07228 or U.S. Pat. No. 5,660,922(Herridge et al.). In a coextrusion technique, various molten streamsare transported to an extrusion die outlet and joined together inproximity of the outlet. Extruders are in effect the “pumps” fordelivery of the molten streams to the extrusion die. The preciseextruder is generally not critical to the process. A number of usefulextruders are known and include single and twin screw extruders, andbatch-off extruders. Conventional extruders are commercially availablefrom a variety of vendors such as Davis-Standard Extruders, Inc.(Pawcatuck, Conn.), Black Clawson Co. (Fulton, N.Y.), Berstorff Corp.(NC), Farrel Corp. (CT), and Moriyama Mfg. Works, Ltd. (Osaka, Japan).

Films of the present invention are optionally annealed to minimize oreliminate necking in the film, to relieve asymmetric stresses in thefilm that give rise to shrinking, and to improve the dimensionalstability. Commonly, the films are coextruded and then they are run overhot rolls, through a heated oven or subjected to an IR heater. It isdesirable to heat treat the films under minimal tension so that theasymmetric stresses are relieved.

For some applications, it is preferred that the film or packageconforms, at least substantially, to the shape of the contained product.Often, the film heat shrinks under cook-in conditions to form a tightlyfitting package. Alternatively, the cook-in film package can be causedto shrink around the contained food product prior to initiating thecook-in procedure by, for example, placing the package in a heatedenvironment prior to cooking.

The films of the present invention are optionally oriented, eitheruniaxially (that is, substantially in one direction) or biaxially (thatis, substantially in two directions), if so desired. Such orientationcan result in improved strength properties, as evidenced by highermodulus and tensile strength. Optionally heat-setting at a selectedtemperature may follow the orienting step.

In addition, for purposes of the present invention, the processingtemperature advantageously will not exceed the temperature at whichthermal degradation of the olefin unsaturated ester copolymer,photoinitiator or crosslinking enhancer occurs. In some cases, suchdegradation would result in scorched compositions due to formation offree radicals. Thermally-induced fragmentation of the initiator withinthe processing equipment can result in premature crosslinking. In otherinstances, slow curing compositions would result from inactivation ofthe initiator. Degradation temperatures differ for each olefinunsaturated ester copolymer, photoinitiator or crosslinking enhancer.Depending upon the type of polymer and the amount of additives, theprocessing temperature often conveniently ranges from between 140° C.and 250° C.

Methods of making multicomponent structures of the Invention are withinthe skill in the art. Regardless of the method used to make themulticomponent structure, including multilayer film of the invention,there are steps of providing a composition comprising at least oneolefin unsaturated ester copolymer and at least one compound selectedfrom the group comprising photoinitiators and crosslinking enhancers,which providing may include admixing the copolymer and compound.Preferably during production or, alternatively, between initialproduction and use, or both, the multicomponent structure or film istreated or irradiated with UV radiation.

The thickness of a multilayer film according to the practice of theinvention is advantageously at least 20, preferably at least 50 micronsand preferably less than 300, more preferably less than 100 micronsthick (2×10⁻⁵, 3×10⁻⁵, 3×10⁻⁴, 1×10⁻⁴ m, respectively).

The invention is applicable to the use of a tie layer of the inventiondirectly between at least two parts of a multicomponent structure,referred to herein as layers for convenience. While at least one layer,exemplified by the first layer, advantageously comprises at least onevinylidene chloride polymer, other layers, exemplified herein by thesecond layer, are suitably any material, preferably any material towhich the first layer may exhibit Insufficient adhesion, especiallyunder conditions of elevated temperature. More preferably the secondlayer is one with which the first layer exhibits insufficient interlayeradhesion at elevated temperatures even when a tie layer composed of theolefin unsaturated ester copolymer but without the photoinitiator orphotoinitiator and crosslinking enhancer used in the practice of theinvention or with those components but before exposure to sufficientactinic radiation. In the case of multilayer films, the material can beany material suitable for making film layers therefrom. The material isadvantageously polymeric. The second layer optionally also comprises atleast one vinylidene chloride polymer, which may be of the same or adifferent composition from the first layer. Preferably, however, thesecond layer comprises at least one polymer different from a vinylidenechloride polymer. Such polymers include polyolefins, polyesters,polyamides, and polycarbonates, more specifically polyethylene (PE),medium density polyethylene (MDPE), high density polyethylene (HDPE),low density polyethylene (LDPE), White LDPE, linear low densitypolyethylene (LLDPE), very low density polyethylene (VLDPE),polypropylene (PP), propylene ethylene copolymer (PPE), nylon, ethylenevinyl acetate (EVA), high VA content EVA (for example 12-35 percent byweight VA content EVA), ethylene methyl acrylate copolymer (EMA),ethylene ethyl acrylate copolymer (EEA), ethylene butyl acrylatecopolymer (EBA), high impact polystyrene (HIPS), polyvinyl chloride(PVC), ethylene butene copolymer (EB), maleic anhydride modifiedpolyolefins (wherein “polyolefins” includes EVA), polyethyleneterephthalate (PET), copolymers of PET or CoPET, or an ionomer, forexample, SURLYN (DuPont), or the like, or combinations or mixturesthereof. As to nylon, nylon 6; 11; 12; 6, 12 and 6, 66 are suitable asare commercially available products such as ULTRAMIDKR™ 4600 (BASF),NOVAMID™ 2030 (Mitsubishi Chem. Co.), DURATHANE™ (Farbenfabriken Bayer,A. G.), “1030” (Unitika, Japan), ZYTEL SUPERTUFF™ 811 (DuPont), “4018”(Huels, Germany), and ELY™ 1256 (Elmser, Switzerland). Other suitablecommercially available materials include Exxon 5610 (blend of PPcontaining EVA), Admer™ (Mitsui), for example Admer™ No. AT469C, Bynel™(DuPont), for example Bynel™ E361 or 3036), Plexar™ 3342. Admer™, Bynel™and Plexar™ 3342 polymers are believed to be maleic anhydride modifiedpolyolefins.

In a multilayer film a second layer advantageously has a thickness atleast 3 microns (3×10⁻ m), preferably at least 10 microns (10⁻⁵ m), morepreferably at least 15 microns (15×10⁻⁶ m) to achieve abuse-resistance,sealing, or other properties. The layer is advantageously less than orequal to 100 microns (10⁻⁴ m), preferably less than or equal to 50microns (50×10⁻⁶ m), more preferably less than or equal to 25 microns(30×10⁻⁶ m) for the purpose of providing abuse resistance or sealingproperties.

Skin layer or layers preferably comprise a material selected from one ormore of the layers listed as second layers, preferably isotacticpolypropylene homopolymer (IPP), ethylene propylene block copolymer,ethylene propylene random copolymer (RCP), propylene butene copolymer(PB), ethylene propylene butene terpolymer (EPB), high densitypolyethylene (HDPE), linear low density polyethylene (LLDPE), mediumdensity polyethylene (MDPE), ethylene vinyl alcohol (EVOH), low densitypolyethylene (LDPE), ethylene vinyl acetate (EVA) or combinationsthereof, with the polyethylenes more preferred. If there are two skinlayers, they are optionally the same or different both compositionallyand in thickness.

A multilayer film according to the present invention preferably includesat least one layer having a low permeance to oxygen, preferably anoxygen permeance of no more than (in ascending order of preference) 150cm³/m²·atm·24 hours, 125 cm³/m²·atm·24 hours, 100 cm³/m²·atm·24 hours,75 cm³/m²·atm·24 hours, 50 cm³/m²·atm·24 hours, 30 cm³/m²·atm·24 hours,20 cm³/m²·atm·24 hours, and 10 cm³/m²·atm·24 hours. Such an O₂-barrierlayer can include one or more of the following polymers: EVOH, PVDC,polyalkylene carbonate, polyamide, and polyester; of the foregoing, PVDCis particularly preferred. A barrier layer preferably has the structurepreferred for the PVDC layer previously described.

The multilayer film of the present invention, in another embodiment,includes one or more other layers, preferably from one to fouradditional layers. Such layer(s) optionally serve as inner or outerlayers and are optionally classified as bulk layers, barrier layers,seal layers, or abuse layers. Such a layer optionally includes one ormore polymers described as polyolefins, polyvinylidene chloridepolymers, polyolefin unsaturated ester polymers, polyurethanes,polyamides, polyesters or halopolymers, and preferably include at leastone polymer of at least one C₂-C₁₂ α-olefin, styrene, amide, ester, orurethane. In one embodiment, the film of the present inventionoptionally includes a layer derived, at least in part, from a polyester,a polyamide or combination thereof. This layer is optionally an inner orouter layer as desired. Examples of suitable polyesters includeamorphous (co)polyesters, poly(ethylene/terephthalic acid), andpoly(ethylene/naphthalate), although poly(ethylene/terephthalic acid)with at least 75 mole percent, more preferably at least 80 mole percent,even more preferably at least 85 mole percent, and most preferably atleast 90 mole percent of its mer units derived from terephthalic acidcan be preferred for certain applications.

Where such a layer includes a polyamide, the polyamide optionallyincludes one or more of polyamide 6, polyamide 6/66, polyamide 6,66,polyamide 6.66, polyamide 9, polyamide 10, polyamide 11, polyamide 12,polyamide 66, polyamide 610, polyamide 612, polyamide 61, polyamide 6T,polyamide 69, copolymers made from any of the monomers used to make twoor more of the foregoing homopolymers, and blends of any of theforegoing homopolymers, copolymers or combination thereof.

Such layers have a thickness preferably at least 0.005 mm, morepreferably at least 0.025, most preferably at least 0.05 mm. Thethickness is preferably less than or equal to 1, more preferably lessthan or equal to 0.5, most preferably less than or equal to 0.25 mm. Inmost instances, the thickness is advantageously at least 1, moreadvantageously at least 5, preferably at least 10, more preferably atleast 15, most preferably at least 25, and advantageously up to 70, moreadvantageously to 60, preferably to 50, more preferably to 45, and mostpreferably to 40 percent of the total thickness of a multilayer film.

The present invention also provides a multicomponent structure such as ablow molded container formed from multilayer plastic film having aseries of component layers and at least one bonding layer bonding atleast two of said component layers together, said bonding layercomprising at least one olefin unsaturated ester copolymer and at leastone photoinitiator, an adjacent barrier, preferably polyvinylidenechloride (PVDC) layer, and preferably outer layers preferably comprisinga polyolefin homopolymer, copolymer or ionomer, more preferably anethylene polymer, most preferably a LLDPE.

Preferably, the film according to the present invention comprises atotal of from 2 to 20 layers; more preferably, from 2 to 12 layers; morepreferably, from 2 to 9 layers; more preferably, from 3 to 8 layers.Various combinations of layers can be used in the formation of amultilayer film according to the present invention. Given below are someexamples of preferred combinations in which letters are used torepresent film layers. Although only 2-through 9-layer embodiments areprovided here for illustrative purposes, more or additional layers areoptionally present. Structures of the invention include the followingwhere A is a skin layer, B is a barrier layer or layer having interlayeradhesion characteristics similar to that of a vinylidene chloridepolymer, C is an abuse, bulking or other layer which is appropriatelystiff or flexible and optionally provides additional properties to themultilayer film, and T is a tie layer where at least one layerdesignated “T” comprises at least one olefin unsaturated ester copolymerand at least one photoinitiator. Note that within a structure havingmore than one layer represented by the same letter, the layers maydiffer in composition. For instance, A/A (not an example of theinvention, used for illustrative purposes only) optionally has a firstpolyethylene layer and a second polypropylene layer. Similarly,A/T/B/T/A and A/T2/T1/B/T1/T2/A include films having a first tie layeraccording to the invention and a second tie layer of composition withinthe skill in the art as well as films having two tie layers according tothe practice of the invention which are optionally of the same ordifferent composition. Illustrative structures according to the practiceof the invention include A/T/B, A/T/B/T/A, A/T/B/T/C, A/T/B/C, A/B/T/C,A/T/C/T/B/T/C/T/A, A/T/C/T/B, A/C/T/B, A/C/B/T/C, A/T/B/A, A/T/B/T/C/A,A/T/B/C/A, A/T/C/A, A/T/C/T/B/A, A/C/T/B/A, A/T/C/B/T/C/A, A/T/B/T/A,A/T/B/T/C/T/A, A/T/B/C/T/A, A/B/T/C/T/A, A/T/C/T/B/T/A, A/C/T/B/T/C/T/A,A/C/T/B/T/C/A, A/C/T/B/T/A, as well as variations on each of thesewherein one or more of A, B, C or T is optionally multiple layers suchas A represented by A1/A2, A1/A2/A3, A1/A2/A1, B as B1/B2, B1/B2/B3,B1/B2/B1, C as C1/C2, C1/C2/C3, C1/C2/C1, T as T1/T2, T1/T2/T3, T1/T2/T1or combinations thereof where the layers with numerical designations areoptionally of the same or different composition, at least one T is a tielayer according to the practice of the invention and each numericdesignation of T is either a tie layer according to the practice of theinvention or a tie layer within the skill in the art, all being of thesame or different compositions. The invention includes, for instance,films disclosed in such references as U.S. Pat. Nos. 4,692,361;5,993,922; 6,342,282; 6,379,812; and 6,551,674 wherein at least one tielayer according to the practice of the present invention is added orsubstituted for a tie, bonding or adhesion layer taught in thereference. A vinylidene chloride polymer is advantageously used for alayer, preferably a barrier layer, adjacent at least one tie layeraccording to the practice of the present invention, in the films.

A multilayer plastic film is optionally laminated to a web, preferablybefore cooling.

Regardless of the structure of the multilayer film of the presentinvention, one or more conventional packaging film additives areoptionally included therein. Examples of additives that can beincorporated include, but are not limited to, antiblocking agents,antifogging agents, slip agents, colorants, flavorings, antimicrobialagents, and meat preservatives. The ordinarily skilled artisan is awareof numerous examples of each of the foregoing. Where the multilayer filmis to be processed at high speeds, inclusion of one or more antiblockingagents in, on or in and on one or both outer layers of the filmstructure can be preferred.

Films and other multicomponent structures of the invention areoptionally further treated by means within the skill in the art such asby corona, plasma or both to increase adhesion to meat or the same orother surface-treatment to enhance receptiveness to metallization,coating, printing inks or lamination.

A film of the invention advantageously has an adhesion strength asmeasured according to the procedures of ASTM 904-98 at 93° C.advantageously of at least 50 N/m, more advantageously at least 55 N/m,most advantageously of at least 75, preferably at least 87.5, morepreferably at least 90, most preferably at least 100 and even morepreferably at least 120 N/m. These adhesion strengths are measured aftermanufacture of a multicomponent structure of the invention but beforesubsequent exposure of the structures to temperatures in excess ofambient temperatures.

A film of the invention advantageously can survive exposure to,preferably cooking, without undergoing spontaneous delamination at least65° C., more advantageously at least 70° C., most advantageously atleast 75° C., preferably at least 80° C., more preferably at least 85°C., most preferably at least 90° C., and especially at least 93° C.Advantageously, the film of the present invention is capable ofsurviving exposure to those temperatures for at least 1 minute, moreadvantageously at least 2 minutes, most advantageously at least 5minutes, preferably at least 10 minutes, more preferably at least 20minutes, most preferably at least 60 minutes, and in especially favoredembodiments at least 120 minutes. Although testing is advantageouslydone with a liquid inside a bag of the film, the product being cookedpreferably includes a meat, or other cookable food product, for exampleproteinaceous or plant food products, more particularly fatty foods.While complete avoidance of delamination is the goal, for purposes ofthe invention, a multicomponent structure is considered to survive thestated heat exposure conditions if the structure of the inventionexhibits at least 30, advantageously at least 40, more advantageously atleast 50, most advantageously at least 60, preferably at least 70, morepreferably at least 80, most preferably at least 90 percent fewerdelaminations visible to the unaided eye compared with a multicomponentstructure of the same composition, components and structure except oneof either not having the photoinitiator in the olefin unsaturated estercopolymer composition (tie layer) or not being irradiated with UVradiation.

In a preferred embodiment of the invention a bag is made from the filmof the present invention by sealing to itself an outer layer, wherebythat layer becomes the inside layers of the bag. Such bags includeend-seal bags, side-seal bags, L-seal bags, lap seal bags, or pouches.The film or bag thereof is suitably formed into food packaging, forexample by first forming a bag or casing from the film, introducing theproduct into the bag or casing, then sealing the open side of the bag orcasing. Alternatively, the film of the present invention is wrappedsubstantially completely around the product then heat sealed to form apackage. Optionally, films, bags or packages of appropriate constructionare heat shrunk around the contents of the package. Packages of films orstructures are suitable for exposure to temperatures suitable forcooking or other heat treatment of the packaging and contents.

In addition to use in food packaging, especially retort and hot fillapplications, practice of the invention is useful in formation of anymultilayer or multicomponent structure, particularly any such structuresuitable for high temperature application where delamination would bedisadvantageous. Special application is found in coextrusion ofstructures with polyvinylidene chloride layers or other layers havingother halogen-containing polymers, especially ones that demonstratedelamination. Additionally, practice of the invention is useful inpreparing such items as clothing and tents, especially flame retardantitems, which are within the skill in the art such as disclosed byRomanowski in U.S. Pat. No. 5,811,359.

Objects and advantages of this invention are further illustrated by thefollowing examples. The particular materials and amounts thereof, aswell as other conditions and details, recited in these examples shouldnot be used to limit this invention. Unless stated otherwise allpercentages, parts and ratios are by weight.

EXAMPLES 1-6 AND COMPARATIVE SAMPLE C Enhancement of 93° C.Peel-Adhesion Strength of Benzophenone-Modified EVA Tie Layer with UVIrradiation

Preparation of tie-layer material: Benzophenone at a level of 2 weightpercent is incorporated into Elvax 3190 ethylene vinyl acetate having 25percent vinyl acetate and melt index (MI) determined according to theprocedures of ASTM D-1238 (190° C./2.16 kg) of 2 (commercially availablefrom DuPont) by twin screw extrusion compounding with a counter-rotatingtwin crew extruder at a melt temperature of 150° C. This 2 weightpercent benzophenone modified EVA is used undiluted in coextrusion forExamples 1-3, and diluted to a 1 weight percent benzophenone EVAcomposition before coextrusion in a Examples 4-6.

Coextrusion of Multi-Layer Structures:

The following five-layer coextrusion structures (Skin/Tie layer/PVDC/Tielayer/Skin) are made using a multi-extruder coextruslon system. Allfilms have thicknesses of 6 mil (152.4 micron). Each skin layer is 40percent of the total thickness. Each tie layer is 5 percent of the totalthickness, and the PVDC core is 10 percent of the total thickness.

Sample A:

-   -   Skin layers=A LLDPE with MI=5.5, Density=0.921 commercially        available from The Dow Chemical Company under the trade        designation Dowlex 3010, hereinafter LLDPE-1    -   Tie layers=EVA+2 weight percent benzophenone prepared previously    -   PVDC=A PVDC copolymer of vinylidene chloride and 7.75 weight        percent methyl acrylate, hereinafter referred to as PVDC-1

Sample B

-   -   Skin layers=LLDPE-1    -   PVDC=PVDC-1    -   Tie layer=EVA+1 weight percent benzophenone as previously        prepared

Sample C:

-   -   Skin layers=A LDPE with MI=1.9, Density=0.926 commercially        available from The Dow Chemical Company under the trade        designation Dow LDPE 535I hereinafter LDPE-2    -   Tie layers=EVA unmodified (without added benzophenone)    -   PVDC=PVDC-1

Sample D:

-   -   Skin layers=LDPE-2    -   Tie layers=EVA containing 1 weight percent benzophenone    -   PVDC=PVDC-1

Irradiation of Coextrusion Multi-Layer Structures

The UV irradiation source is a H-type UV bulb with an effective lengthof 8 inches (0.2032 m) long. The total energy output of the bulb is 4800watts. The entire output of the UV source is focused onto an area of 4inches by 6 inches (0.1016 m by 0.1524 m).

Samples A, B, C and D are cut into test strips of 1 inch (0.0254 m) wideand 6 inches (0.1624 m) long. Samples A, B, and D are UV irradiated.Sample C is not irradiated. The sample strips to be UV irradiated areplaced into the area of irradiation of the UV source. The time ofexposure to the UV light is controlled by a shutter. Each strip isirradiated on both sides for the same amount of time.

Peel-Adhesion Testing:

The test strips are first folded over and heat-sealed using a JBInstruments Hot Tack Tester. The polyolefin skin layers heat sealtogether. The temperature of the upper and lower sealed bars are set at150° C., with a sealing time of 0.85 sec and a sealing pressure ofpressure of 0.27 N/mm².

A small amount of acetone is applied with a cotton swab to the sealedarea and force is applied manually by pulling on opposite sides of theseal to cause delamination in the tie-layer. The delaminated portion isthen extended to an inch (0.0254 m) long to allow for gripping on theInstron MTS Renew Universal Tensile Model 1123 tester, with a test speedof 10 inches per minute (0.0042 m/sec) for peel-adhesion testing. Afterthe acetone is dried, the two delaminated surfaces are gripped in anInstron for a peel test at 93° C. This peel-adhesion test is inconformance to ASTM F904-98. The force required to propagate thedelamination was recorded as the peel-adhesion value.

Results: The Peel-Adhesion at 93° C. value of the irradiated Samples A,B, and D, and that of the un-irradiated Sample C are listed in Table 1.

TABLE 1 93° C. Peel-Adhesion Test Results of UV IrradiatedBenzophenone-modified EVA Tie-Layers UV Irradiation Adhesion AdhesionStd. Example Time/side, sec Sample N/m Dev., N/m 1 1 A 124.86 25.57 2 2A 96.67 28.54 3 5 A 105.42 35.90 4 1 B 153.05 31.00 5 2 B 182.30 96.60 65 B 142.72 27.32 C* 0 C 22.06 11.74 7 1 D 97.19 8.41 8 2 D 102.97 13.489 5 D 86.16 25.92 *Not an example of the invention

From the results in Table 1, it can be seen that adding benzophenone atboth 1 weight percent and 2 weight percent to the tie-layer EVA,followed by UV irradiation of the film, causes a significant improvementin the 93° C. peel-adhesion test results over thenon-benzophenone-modified, non-UV-irradiated EVA tie layer material.Comparison of Examples 7, 8 and 9 with Examples 1-6 also shows that datais comparable for multilayer films having LDPE-1 and LDPE-2 as skinlayers. This is expected since the composition and density are similarand the interfacial interaction with the EVA corn position would beexpected to be very similar.

EXAMPLES 10-15 AND COMPARATIVE SAMPLE F Enhancement of 93° C.Peel-Adhesion Strength of Benzophenone Modified EMA Tie Layer with UVIrradiation

Preparation of tie-layer material: 2 weight percent of benzophenone isincorporated into ethylene methyl acrylate polymer having 29 percentmethyl acrylate and melt index of 3 determined as in Example 1commercially available from Atofina Chemical under the trade designationLotryl™ 29MA03 (EMA-1) by twin screw extrusion compounding with acounter-rotating twin screw extruder at a melt temperature of 150° C.This 2 weight percent benzophenone-modified EMA is used undiluted forSample D and used after dilution to 1 weight percent benzophenonecontent for Sample E.

Coextrusion of Multi-Layer Structures:

The following five layer coextrusion structures (Skin/Tie layer/PVDC/Tielayer/Skin) are made using a multi-extruder coextrusion system. Allfilms have a thickness of 6 mil (152.4 micron). Each skin layer is 40percent of the total thickness. Each tie layer is 5 percent of the totalthickness, and the PVDC core is 10 percent of the total thickness.

Sample E:

-   -   Skins=LLDPE-1    -   Tie layers=EMA-1 containing 2 weight percent benzophenone        previously prepared    -   PVDC=PVDC-1

Sample F:

-   -   Skin layers=LLDPE-1    -   PVDC=PVDC-1    -   Tie layer=EMA-1 containing 1 weight percent benzophenone        previously prepared

Sample G:

-   -   Skin layers=LOPE-2    -   Tie layers=EMA-1 unmodified (without added benzophenone)    -   PVDC=PVDC-1

For irradiation of coextrusion multi-layer structure Samples E, F, and Gare cut as in Example 1. Samples E and F are Irradiated as in Example 1.The test strips are prepared and tested as in Example 1.

Results: The Peel-Adhesion at 93° C. value of the irradiated samples Eand F and that of the un-irradiated sample G are listed in Table 2.

TABLE 2 93° C. Peel-Adhesion Test Results of UV IrradiatedBenzophenone-modified EMA Tie-Layers UV Time/ Adhesion side AdhesionStd. Dev., Example (sec) Sample N/m N/m 10 1 E 59.37 19.44 11 2 E 75.839.81 12 5 E 69.35 8.23 13 1 F 94.56 13.66 14 2 F 95.43 22.94 15 5 F75.65 31.52 G* 0 G 38.88 14.01 *Not an example of the invention

From the results in Table 2, it can be seen that adding benzophenone atboth 1 weight percent and 2 weight percent to the tie layer EMA,followed by UV irradiation of the film, causes a large degree ofimprovement in the 93° C. peel-adhesion test results over thenon-benzophenone modified, non-UV irradiated EMA tie layer material

EXAMPLE 16 AND COMPARATIVE SAMPLE H

The procedure of Example 10, Sample E, is repeated except that the EMAis different and contains 0.05 weight percent benzophenone for Sample Hand the resulting film is exposed to UV radiation using the sameequipment as used in preparing Sample E. The EMA is a mixture of 71.45weight percent of EMA-1 and 28.5 weight percent of a resin having 24percent by weight methyl acrylate and 76 percent by weight ethylene,having a melt index of 0.5 determined as in Example 1, commerciallyavailable from Atofina under the trade designation LOTRYL 24MA005. Themixture is referred to herein as EMA-2.

Sample H:

-   -   Skin layers=LDPE-1    -   Tie layers=EMA-2 containing 0.05 weight percent benzophenone    -   PVDC=PVDC-1

Results: The Peel-Adhesion test is performed as in Example 1 and thevalues are listed in Table 3.

TABLE 3 93° C. Peel-Adhesion Test Results of UV IrradiatedBenzophenone-modified mixed EMA Tie-Layers UV Irradiation AdhesionAdhesion Std. Example Time, sec per side Sample N/m Dev., N/m 16 2 H 17576 H* 0 H 18 1 *Not an example of the invention

The data in Table 3 show that a mixture or blend of olefin unsaturatedester copolymers, particularly of olefin copolymers with alkyl esters ofunsaturated acids, more particularly of ethylene and alkylmethacrylates, having different characteristics such as amount ofunsaturated acid monomer, melt index or its associated molecular weight,or both, exhibits very useful results in the practice of the invention.

EXAMPLE 17 AND COMPARATIVE SAMPLE K

The procedure of Example 4, Sample B, is repeated except that the EVAcontains 1000 parts per million (ppm) benzophenone for Sample J and theresulting film is exposed to UV radiation using the same equipment asused in preparing Sample B. The 2 weight percent benzophenone modifiedEVA is diluted in a 20:1 ratio with EVA to produce the 1000 ppmbenzophenone concentration. The following samples are prepared:

Sample J:

-   -   Skin layers=LDPE-2    -   Tie layers=EVA containing 1000 ppm benzophenone    -   PVDC=PVDC-1

Sample K:

-   -   Skin layers=LDPE-2    -   Tie layers=EVA with no benzophenone    -   PVDC=PVDC-1

Results: The Peel-Adhesion test is performed as in Example 1 and thevalues are listed in Table 4.

TABLE 4 93° C. Peel-Adhesion Test Results of UV IrradiatedBenzophenone-modified EVA Tie-Layers UV Irradiation Adhesion AdhesionStd. Example Time, sec per side Sample N/m** Dev., N/m 17 2 J 125.0323.64 K* 0 K 24.69 1.96 *Not an example of the invention **Convertedfrom lb/in at 175.118 N/m per lb/in

The data in Table 4 show that amounts of photoinitiator in the 1000parts per million range are still very effective in achieving increasedadhesion.

EXAMPLE 18-21 AND COMPARATIVE SAMPLE L

Samples L trough Q are prepared as Sample B except using high densitypolyethylene (HDPE) skin layers and the amounts of benzophenone listedin Table 5. Samples R and S are prepared as Sample H using the samemixture of EMA polymers, except using the HDPE skin layers. Samples Lthrough S are coextruded having the following structures:

Samples L through Q:

-   -   Skin layers=A high density polyethylene (HDPE with melt        index=1.0, Density=0.962 g/cm³ commercially available from        Equistar under the trade designation ALATHON 6210 (hereinafter        HDPE-1).    -   Tie layers=EVA containing the weight percent benzophenone        indicated in Table 5    -   PVDC=PVDC-1

Samples R and S:

-   -   Skin layers=HDPE-1    -   Tie layers=EMA-2 containing the weight percent benzophenone        indicated in Table 5    -   PVDC=PVDC-1

The Samples are irradiated and cut as in Example 1. The samples aretested for peel adhesion as in Example 1 except at 100° C.

Results: The Peel-Adhesion values of the irradiated Samples L through Sat 100° C. are listed in Table 5.

TABLE 5 100° C. Peel-Adhesion Test Results of UV IrradiatedBenzophenone-modified EVA Tie-Layers UV Irradiation Benzo- AdhesionTime/ phenone Adhesion Std. Dev., Example side, sec concentration SampleN/m N/m L* 2 0 L 12.96 0.7 18 2 0.05 M 52.54 35 19 2 0.1 N 59.54 24.5 202 0.25 P 113.83 31.5 21 2 0.5 Q 157.61 54.3 22 2 0.05 R 175.12 24.5 23 20.1 S 152 35 *Not an example of the invention **Converted from lb/in at175.118 N/m per lb/in

The data in Table 5 shows a 300 percent improvement using even 0.05weight percent photoinitiator and 2 seconds irradiation over comparativesample L when the tie layer is an ethylene vinyl acetate. Increasing theamount of photoinitiator or using a mixed melt index ethylene methylacrylate as the olefin unsaturated ester copolymer improves the results,showing as much as a 1200 percent improvement in adhesion strengthmeasured at 100° C. over sample L where EVA is the olefin unsaturatedester copolymer. To assist in comparison, note that an adhesion valueobtained at 100° C. indicates better adhesion than the same valueobtained at 93° C.

While the invention is explained in terms of olefin unsaturated estercopolymers, it is expected that tie layers within the skill in the artsuch as thermoplastic polyurethane, maleic anhydride grafts ofpolyolefin homopolymers and copolymers and chlorinated polyethylenecould be similarly admixed with a photoinitiator and optionally acrosslinking enhancer and irradiated with actinic radiation of awavelength appropriate for the photoinitiator to increase the adhesionstrength over the tie layer without either the photoinitiator or theirradiation.

1. A multicomponent structure comprising at least two components, afirst and a second component, having a tie layer directly between them,the tie layer comprising at least one olefin unsaturated ester copolymerand at least one photoinitiator, wherein at least the first componentincludes a majority of a vinylidene chloride polymer or combination ofvinylidene chloride polymers (hereinafter PVDC component) wherein thestructure has increased interlayer adhesion strength measured accordingto ASTM F904-98 at 93° C. after irradiation with UV radiation ascompared with the interlayer adhesion strength before treatment with theUV radiation.
 2. The structure of claim 1 in the form of a multilayerfilm.
 3. The structure of claim 1 wherein at least one second componentcomprises at least one polymer, glass, silica, paper, metal, fabric orcombination thereof.
 4. The structure of claim 1 wherein the secondcomponent comprises a polymer selected from at least one vinylidenechloride polymer, which may be of the same or a different compositionfrom the first component or layer, or at least one polymer selected frompolyolefins, polyesters, polyamides, and polycarbonates, polyethylene(PE), medium density polyethylene (MDPE), high density polyethylene(HDPE), low density polyethylene (LDPE), White LDPE, linear low densitypolyethylene (LLDPE), very low density polyethylene (VLDPE),polypropylene (PP), propylene ethylene copolymer (PPE), nylon, ethylenevinyl acetate (EVA), EVA having 12-35 percent by weight VA content,ethylene methyl acrylate copolymer (EMA), ethylene ethyl acrylatecopolymer (EEA), high impact polystyrene (HIPS), polyvinyl chloride(PVC), ethylene butene copolymer (EB), maleic anhydride modifiedpolyolefins (wherein “polyolefins” includes EVA), polyethyleneterephthalate (PET), copolymers of PET, or an ionomer, or combinationthereof.
 5. The structure of claim 1 wherein the olefin unsaturatedester copolymer comprises at least one ethylene/ethyl acrylate copolymeror at least one ethylene/methyl acrylate.
 6. The structure of claim 1wherein the olefin unsaturated ester copolymer comprises at least twoolefin unsaturated ester copolymers.
 7. The structure of claim 6 whereinat least two olefin unsaturated ester copolymers comprise the sameolefin and unsaturated ester copolymers of the same type, that isunsaturated esters having unsaturated acid moieties or havingunsaturated alcohol moieties differing in melt index by at least 1 g/10min.
 8. The structure of claim 1 wherein the photoinitiator is selectedfrom the group consisting of aromatic ketones, aromatic monoacetals of1,2-diketones, aromatic α-hydroxy ketones, quinones, organic peroxides,azo compounds, nitroso compounds, acyl halides, hydrozones, mercaptocompounds, pyrylium compounds, triacylimidazoles, acylphosphine oxides,bisimidazoles, chloroalkyltriazines, benzoin ethers, benzyl ketals,thioxanthones, and mixtures thereof.
 9. The structure of claim 8 whereinthe photoinitiator is selected from aromatic ketones, monoacetals of1,2-diketones or mixtures thereof.
 10. The structure of claim 1 whereinat least one crosslinking enhancer is present.
 11. The structure ofclaim 10 wherein the crosslinking enhancer is selected from the groupconsisting of triallyl cyanurate, triallyl isocyanurate, pentaerythritoltriallyl ether, pentaerythritol triacrylate, pentaerythritoltetraacrylate, pentaerthritol tetramethacrylate, dipentaerythritolpentaacrylate, ethylene glycol diacrylate, ethylene glycoldimethacrylate, tetraethylene glycol diacrylate, 1,4-butanedioldiacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol diacrylate,1,6-hexanediol dimethacrylate, methoxy-1,6-hexanediolpentaerythritoltriacrylate, trimethylolpropane triacrylate, trimethylolpropanetrimethacrylate, diallyl maleate, dipropargyl maleate, dipropargylmonoallyl cyanurate, polymethacrylate urethanes, polymeric epoxyacrylates, polyester acrylate monomers and oligomers,poly-n-butyleneoxide glycol diacrylates, and bisphenol A alkylene oxideadduct diacrylates and combinations thereof.
 12. The structure of claim1 further comprising an additional layer or component comprising apolymer comprising mer units derived from at least one member of thegroup consisting of C₂-C₁₂ α-olefin, styrene, amide, ester, urethane(isocyanates, amine, or hydroxyl), and combinations thereof.
 13. Thestructure of claim 1 which has from 3 to 11 components or layers. 14.The structure of any of claims 1-13 in the form of a film, bag, pouch,tube, casing, lined pipe, coextruded pipe, sheet, lidstock, package orcontainer; a cook-in, hot-fill, or retortable film, bag, container orpackage; a blow molded structure; or a combination thereof.
 15. Thestructure of any of claims 1-13 wherein the effect of irradiation isshown by at least one of (a) the components in the presence of the tielayer have an adhesion strength measured according to ASTM F904-98 at93° C. of at least 50 N/m after the structure has been irradiated withUV radiation, as compared with an adhesion strength of less than 40 N/mbefore irradiation; (b) the increase in adhesion strength measuredaccording to ASTM F904-98 at 93° C. before and after irradiation is atleast 20 N/m or 30 percent of the adhesion strength before irradiation;or (c) the first and second components separated by the tie layer afterirradiation exhibit at least 50 percent fewer spontaneous delaminationfailures after commercial processing which involves exposure to at leastone of: a temperature of at least 65° C. for a period of at least 5minutes, a temperature of at least 80° C. for a period of at least 2minutes, a temperature of at least 85° C. for a period of at least 5minutes, or a temperature of at least 93° C. for a period of at least 1minute as compared with a structure of the same composition, componentsand configuration but without the photoinitiator, the irradiation orboth and exposed to the same temperature for the same time period.
 16. Amethod of cooking a food product comprising: a) substantially completelysurrounding the food product in the structure of any of claims 1-13 toform a packaged food product, and b) subjecting the packaged foodproduct to an elevated temperature sufficient to cook the food product.17. A method for adhering a first layer to a second layer in a filmcomprising a plurality of superimposed layers, the method comprising: 1)coextruding first and second layers, the first layer comprising at least80 percent of a vinylidene chloride polymer; and, directly between thefirst and second layers, a third layer comprising a base polymer havingat least one olefin unsaturated ester copolymer and at least onephotoinitiator; 2) forming a film comprising the layers; and 3)irradiating the film with UV irradiation sufficiently to increase theadhesion strength between the first and second layers.
 18. A method forimproving the adhesion between a first layer or structure comprising avinylidene chloride polymer and a contiguous second layer or structureof the same or different composition, wherein the method includesinterposing directly between the first and second layer a compositioncomprising at least one olefin unsaturated ester copolymer and at leastone photoinitiator and irradiating the composition with sufficient UVradiation to increase the adhesion.
 19. The use of a compositioncomprising at least one olefin unsaturated ester copolymer and at leastone photoinitiator as a tie layer directly between a first component anda second component, which components have an adhesion strength beforeirradiation of less than 40 N/m, treated by UV irradiation, wherein theeffect of the photoinitiator and irradiation is shown by at least one of(a) the components in the presence of the tie layer have an adhesionstrength measured according to ASTM F904-98 at 93° C. of at least 50 N/mafter the structure has been irradiated with UV radiation, as comparedwith an adhesion strength of less than 40 N/m before irradiation or (b)the first and second components separated by the tie layer afterirradiation exhibit at least 50 percent fewer spontaneous delaminationfailures after commercial processing which involves exposure to at leastone of: a temperature of at least 65° C. for a period of at least 5minutes, a temperature of at least 80° C. for a period of at least 2minutes, a temperature of at least 85° C. for a period of at least 5minutes, or a temperature of at least 93° C. for a period of at least 1minute as compared with a structure of the same composition, componentsand configuration but without the photoinitiator, the irradiation orboth and exposed to the same temperature for the same time period.